Purpose: To create an easily applicable system based on a combination of the quantitative level of IMP3 (an oncofetal protein) and tumor stage to more accurately predict postoperative metastasis of localized renal cell carcinoma.

Experimental Design: Three hundred sixty nine patients with localized renal cell carcinoma (without metastasis during nephrectomy) were investigated by the use of survival analysis. The expression of IMP3 was evaluated by immunohistochemistry and quantitated with a computerized image analyzer. Based on combining quantitative IMP3 results with tumor staging (QITS system), patients were divided into four distinct risk groups for the development of metastasis.

Results: The four groups of patients in the QITS system showed significant differences in their metastasis-free (P < 0.0001) and overall survivals (P < 0.0001). Almost all patients of group IV with localized renal cell carcinomas developed metastasis and died after nephrectomy. The 5- and 10-year metastasis-free survival rates for the QITS groups were as follows: for group I, 97% and 91%; II, 62% and 55%; III, 46% and 19%; and IV, 17% and 4%, respectively. The 5- and 10-year overall survival rates for the QITS groups were as follows: for group I, 89% and 72%; II, 58% and 41%; III, 38% and 17%; and IV, 14% and 4%, respectively.

Conclusions: The QITS is a simple and accurate system for the prediction of tumor metastasis. This system not only provides important prognostic information but also can be used at initial diagnosis of localized renal cell carcinoma to identify high-risk patients who may benefit from early systematic therapy.

Renal cell carcinoma (RCC) accounts for ∼85% of all malignant kidney tumors in the United States, making it the most common type of kidney cancer (1, 2). The incidence of this type of carcinoma has been increasing steadily (3). It was expected that ∼51,190 new cases of kidney cancer were diagnosed in the United States in 2007 with ∼12,890 mortalities (4).

Currently, nephrectomy is the standard of care for almost all patients with renal cell carcinoma (1, 2, 5). After nephrectomy, patients with metastatic disease typically receive systemic treatment. Recently, three new drugs have been used for treatment of patients with metastatic renal cell carcinoma. Nexavar (sorafenib) and Sutent (sunitinib), the multikinase receptor inhibitors, can block the signaling cascade of the vascular endothelial growth factor (2, 3) and R1, as well as platelet-derived growth factor that are critical to angiogenesis (69). Temsirolimus inhibits the mammalian target of rapamycin complex 1 kinase that regulates protein translation (10). Currently, these new drugs have been used as frontline therapy for patients with clinically metastatic RCC (610). It would be of interest to test whether the kinase inhibitors would benefit patients with localized RCC that were at high risk for metastasis. There is the ASSURE Trial being initiated to evaluate the role of adjuvant therapy with Sunitinib or Sorafenib in patients with high-risk and localized RCC. However, the metastastic potential of localized tumors is often unpredictable.

One of the critical issues is that localized renal cell cancers that are typically classified at the same stage exhibit markedly different biological behavior (1114). Consequently, only 30% of patients with a localized tumor at the time of surgery will subsequently recur and metastasize, and the survival rates of these are typically <10% (15, 16).

An accurate system for the prediction of patient metastasis will allow for better selection of patients who are most likely to benefit from adjuvant therapy, although sparing patients from the side effects of systemic treatment if they are less likely to suffer metastasis after nephrectomy. Currently, evaluation of patients for postnephrectomy adjuvant therapy relies mainly on the Tumor, Nodes, and Metastasis (TNM) staging system (1114, 17). Recently, comprehensive integrated staging systems, using multiple clinical and pathologic predictors, have been proposed (17). They contain different clinical and pathologic risk factors with multiple variables (17). A system using a combination of clinical predictors with biomarker expression profile has been proposed and has shown significantly more accurate than a model combining only standard clinical predictors (18).

Recently, we have discovered that IMP3, an oncofetal protein, is expressed in a subset of renal cell carcinomas, and its expression predicts remarkably well which localized RCCs will subsequently metastasize (19). IMP3 is an oncofetal protein that is a member of a family of conserved RNA-binding proteins that consists of IMP1, IMP2, and IMP3 (20). These IMP proteins contain two RNA recognition motifs and (4) K-homology domains that allow them to bind RNAs with high avidity and specificity; however, only a few specific RNA targets, such as insulin-like growth factor, have thus far been identified (21, 22). IMP3 is expressed in developing epithelium, muscle, and placenta during early stages of human and mouse embryogenesis, but it is expressed at low or undetectable levels in adult tissues (20, 22). A number of cancers have been shown to express IMP3, (21, 23, 24) although cancer cell proliferation and tumor invasion are associated with the expression of IMP3 (25, 26).

In this study, we used a computerized image analyzer [Automated Cellular Imaging System (ACIS)] to quantitatively analyze the expression of IMP3 in localized RCCs. We determined whether tumors with higher levels of IMP3 progressed more rapidly than those with lower levels of this molecule, and whether combining the levels of IMP3 expression and tumor stage could serve as a new system to accurately predict metastasis of localized renal cell carcinoma.

Patients and tumor specimens. Formalin-fixed, paraffin-embedded samples from 369 localized primary renal cell carcinoma patients, who underwent radical or partial nephrectomy, were obtained from the archival files at the University of Massachusetts Medical Center (n = 144), the Massachusetts General Hospital (n = 147), and the City of Hope National Medical Center (n = 78). The data from these sources represented all patients for whom archival tissues and adequate clinical follow-up information were readily available. All cases were collected between January of 1989 and December 2003, and the diagnoses were confirmed by at least two pathologists. Staging was based on pathologic findings following the American Joint Committee on Cancer staging manual, sixth edition, 2002. Two hundred fifteen patients (pT1a or b) were stage I, 63 patients (pT2) were stage II, and 91 patients (pT3a, N0, n = 62; pT3b, N0, n = 29) were stage III. Follow-up for this retrospective study was carried out by reviewing the patients' clinical records. Overall survival was measured from the date of nephrectomy to the date of death, or was censored as the date of the last follow-up visit for survivors. Metastasis-free survival was measured from the date of surgery to the date of the first clinical evidence of metastasis, and was censored at the date of death or the date of the last follow-up visit for survivors. The median follow-up was 63 mo (range, 1-174 mo). The Institutional Review Board at each institution approved this study.

Immunohistochemical analysis. Immunohistochemical studies were done on the DAKO Autostainer (DAKO Corporation) using 5-μm sections of formalin-fixed, paraffin-embedded tissue from nephrectomy specimens by using an avidin-biotinylated peroxidase complex system in a previously published protocol (24). Sections of pancreatic carcinoma with known positivity for IMP3 were used as positive controls for the L523S mouse monoclonal antibody specific for IMP3/KOC (Corixa Corporation) staining. Negative controls were done by replacing the primary antibody with nonimmune IgG.

Quantitative analysis of immunostaining. A total of 1,845 tumor areas (5 different areas per case) from all RCC tissues were quantitatively analyzed by a computerized image analyzer (ACIS; ChromaVision Medical System, Inc.) to evaluate the immunohistochemical results. With ACIS, positive staining was calculated by applying two thresholds, with one recognizing the blue background (hematoxylin stained) cells and another recognizing the brown-positive cells. The integrated optical density is the total sum of brown pixels times the brown intensity of those pixels. The ACIS values were calculated as integrated optical density divided by the sum of the blue area and the brown area. IMP3 expression in RCCs was considered to be either negative (average ACIS value per case, <1) or positive (average ACIS value per case, ≥1).

Statistical analysis. Age, sex, size of the tumor, tumor stage and grade, and IMP3 status were collected as baseline variables. The distribution of each baseline variable was compared for IMP3-positive and IMP3-negative subgroups with the Wilcoxon rank-sum test for continuous variables and the Fisher's exact test for categorical variables. Overall survival and metastasis-free survival of 369 patients were estimated by the Kaplan-Meier method and evaluated with the use of log-rank test for univariate analysis. The Cox proportional hazard model was used to assess the simultaneous contribution of the following baseline covariates of age, sex, size of the tumor, tumor stage and grade, and IMP3 status. A two-sided P value of <0.05 indicated statistical significance. Based on a Cox proportional-hazard model, IMP3 status and tumor stage were the two most important independent risk factors for predicting metastasis of localized RCC; the levels (low versus high) of IMP3 expression from ACIS analysis and tumor stage were divided into four subgroups, each of which had a significantly increasing risk of metastasis and death over the previous one.

The results of quantitative immunohistochemistry showed significant differences in IMP3 staining values between positive (ACIS values, ≥1) and negative (ACIS values, <1) cases (P < 0.0001). The average of the ACIS values was 16.92 ± 24.80 in IMP3-positive RCCs and 0.08 ± 0.09 in IMP3-negative RCCs (P < 0.001). Figure 1 shows a bimodal pattern in which an ACIS value of 10 was a differentiating number for these two groups. Therefore, we used an ACIS value of 10 to divide two groups of patients with high levels (ACIS values, >10) of IMP3 expression (n = 16; average ACIS value, 45.05 ± 32.64) and low levels (n = 33; ACIS values, 1-10) of IMP3 expression (average ACIS value, 3.29 ± 2.20; P < 0.001). Three hundred and twenty patients with localized RCCs were found without expression of IMP3. Eighty six percent (42 of 49) of patients with IMP3 expression in their primary RCCs subsequently developed metastasis (median follow-up, 36 months; range, 1-155 months), whereas 14% (44 of 320) of patients without expression of IMP3 in their primary tumors were found to have metastases after surgery (median follow-up, 71 months; range, 1-174 months).

Fig. 1.

Scatter graph showing automated cellular imaging system (ACIS) values of low and high levels of IMP3 expression in localized RCCs.

Fig. 1.

Scatter graph showing automated cellular imaging system (ACIS) values of low and high levels of IMP3 expression in localized RCCs.

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To determine which risk factors should be incorporated into our predictive algorithm, we did multivariate Cox proportional hazards regression analysis of 369 patients with localized RCCs for all risk factors including IMP3 status (positive versus negative), age, sex, tumor stage, grade, size, and subhistologic type. IMP3 status, tumor stage, and size were observed as independent significant risk factors for metastasis-free survival (data not shown). In addition, we found through Kaplan-Meier curves that patients with low IMP3 expression had better metastasis-free and overall survival rates than patients with high IMP3 expression. Therefore, we decided to combine quantitative IMP3 expression with the tumor TNM stage, which includes tumor size, for our Quantitative IMP3 and Tumor Stage (QITS) system for predicting tumor metastasis and survival. Table 1 lists QITS categorization of four different risk groups. QITS group I was patients with TNM stage 1 and 2, and IMP3-negative tumors; QITS group II patients with TNM stage 3 and IMP3-negative tumors; QITS group III patients with TNM stage 1 and low level of IMP3 tumors; QITS group IV patients with all TNM stages and high level of IMP3 tumors, and patients with TNM stage 2 and 3, and low level of IMP3 tumors (Table 1). QITS group I has the lowest risk, whereas QITS group IV has the highest risk for the development of metastasis after nephrectomy. Of 369 patients, 249 (68%) were group I, 71 (19%) were group II, 16 (4%) were group III, and 33 (9%) were group IV patients. Table 2 provides the relevant clinical characteristics of the 369 patients in the four risk groups. Gender, and tumor histologic type were not correlated with the four risk groups. QITS groups were associated with tumor size (P < 0.0001) and grade (grade 1 and 2 versus grade 3 and 4, P < 0.0001), and age (P = 0.015).

Table 1.

QITS categorization of localized RCCs

QITS groupsIMP3 Status in RCCTNM stageNo of patients
IMP3 negative Stage 1 and 2 249 
II IMP3 negative Stage 3 71 
III IMP3 positive, low level Stage 1 16 
IV IMP3 positive, low-level Stage 2 and 3 33 
 IMP3 positive, high level Stage 1, 2, and 3  
QITS groupsIMP3 Status in RCCTNM stageNo of patients
IMP3 negative Stage 1 and 2 249 
II IMP3 negative Stage 3 71 
III IMP3 positive, low level Stage 1 16 
IV IMP3 positive, low-level Stage 2 and 3 33 
 IMP3 positive, high level Stage 1, 2, and 3  
Table 2.

Clinicopathologic characteristics of patients with renal cell carcinoma

QITS Groups
P
IIIIIIIV
Age (y) mean ± SD 58.6 ± 14.0 62.9 ± 12.8 67.0 ± 10.4 60.8 ± 10.8 P = 0.015 
Sex      
    Male 148 (59%) 48 (68%) 11 (69%) 25 (76%)  
    Female 101 (41%) 23 (32%) 5 (31%) 8 (24%) P = 0.210 
Tumor Size (cm) mean ± SD 3.3 ± 1.1 3.6 ± 0.6 4.1 ± 1.9 9.9 ± 5.1 P < 0.0001 
Tumor grade      
    1-2 161 (65%) 36 (51%) 5 (31%) 8 (24%)  
    3-4 88 (35%) 35 (49%) 11 (69%) 25 (76%) P < 0.0001 
Histological types      
    Clear cell 185 (74%) 60 (85%) 13 (81%) 27 (82%)  
    Papillary 45 (18%) 8 (11%) 1 (6%) 4 (12%)  
    Chromophobe 19 (8%) 3 (4%) 2 (13%) 2 (6%) P = 0.483 
QITS Groups
P
IIIIIIIV
Age (y) mean ± SD 58.6 ± 14.0 62.9 ± 12.8 67.0 ± 10.4 60.8 ± 10.8 P = 0.015 
Sex      
    Male 148 (59%) 48 (68%) 11 (69%) 25 (76%)  
    Female 101 (41%) 23 (32%) 5 (31%) 8 (24%) P = 0.210 
Tumor Size (cm) mean ± SD 3.3 ± 1.1 3.6 ± 0.6 4.1 ± 1.9 9.9 ± 5.1 P < 0.0001 
Tumor grade      
    1-2 161 (65%) 36 (51%) 5 (31%) 8 (24%)  
    3-4 88 (35%) 35 (49%) 11 (69%) 25 (76%) P < 0.0001 
Histological types      
    Clear cell 185 (74%) 60 (85%) 13 (81%) 27 (82%)  
    Papillary 45 (18%) 8 (11%) 1 (6%) 4 (12%)  
    Chromophobe 19 (8%) 3 (4%) 2 (13%) 2 (6%) P = 0.483 

Kaplan-Meier plots and log-rank tests in all patients (n = 369) with localized disease at the time of surgery showed the stratification by TNM stage (Fig. 2A and C) and the QITS systems (Fig. 2B and D) for predicting patient metastasis and overall survivals. In general, significant difference in metastasis-free survival was observed among three TNM stages (P < 0.0001; Fig. 2A). For comparisons between each pair of two stages (Fig. 2A), there is significant difference in metastasis-free survival between patients with stages 1 and 3 (P < 0.0001), and between patients with stages 2 and 3 (P = 0.0001); there is no significant difference in metastasis-free survival between patients with stages 1 and 2 (P = 0.060). Significant difference in overall survival was observed among three TNM stages (P < 0.0001; Fig. 2C). For comparisons between each pair of two stages (Fig. 2C), there is significant difference in overall survival between patients with stages 1 and 3 (P < 0.0001), and between patients with stages 2 and 3 (P = 0.0001); there is no significant difference in overall survival between patients with stages 1 and 2 (P = 0.441). The stratification trend across all QITS risk groups was statistically significant for both metastasis-free and overall survivals (P < 0.0001; Fig. 2B and D). Almost all patients of group IV with localized RCCs developed metastasis and died after nephrectomy (Fig. 2B and D). The 5- and 10-year metastasis-free survival rates for the QITS groups were as follows for group: I, 97% and 91%; II, 62% and 55%; III, 46% and 19%; and IV, 17% and 4%; respectively (Table 3). The 5- and 10-year overall survival rates for the QITS groups were as follows: I, 89% and 72%; II, 58% and 41%; III 38% and 17%; and IV, 14% and 4%; respectively (Table 4). The 5- to 10-year metastasis-free and overall survival of each QITS risk groups is also significantly different (P < 0.0001; Fig. 2B and C), except for QITS group II, whose survival was borderline significantly different than that of group III (P = 0.055 metastasis-free survival; Fig. 2B; P = 0.053 overall survival; Fig. 2C).

Fig. 2.

Kaplan-Meier analysis of metastasis-free and overall survivals in patients according to TNM stage (A and C) and the QITS (quantitative IMP3 and tumor stage) system (B and D). A, significant difference in metastasis-free survival was observed among three TNM stages (P < 0.0001). For comparisons between each pair of two stages, there is significant difference in metastasis-free survival between patients with stages 1 and 3 (P < 0.0001), and between patients with stages 2 and 3 (P = 0.0001); there is no significant difference in metastasis-free survival between patients with stages 1 and 2 (P = 0.060). B, significant difference in metastasis-free survival was observed among four risk groups of QITS system (P < 0.0001). For comparisons between each pair of two groups, there is significant difference in metastasis-free survival between patients with risk group I and patients with risk group II (P < 0.0001), between patients with risk group I and patients with risk group III (P < 0.0001), between patients with risk group I and patients with risk group IV (P < 0.0001), and between patients with risk group II and patients with risk group IV (P < 0.0001). Borderline significant difference was observed between patients with risk group II and patients with risk group III (P = 0.055). C, significant difference in overall survival was observed among three TNM stages (P < 0.0001). For comparisons between each pair of two stages, there is significant difference in overall survival between patients with stages 1 and 3 (P < 0.0001), and between patients with stages 2 and 3 (P = 0.0001); there is no significant difference in overall survival between patients with stages 1 and 2 (P = 0.441). D, significant difference in overall survival was observed among four risk groups of QITS system (P < 0.0001). For comparisons between each pair of two groups, there is significant difference in overall survival between patients with risk group I and patients with risk group II (P < 0.0001), between patients with risk group I and patients with risk group III (P < 0.0001), between patients with risk group I and patients with risk group IV (P < 0.0001), and between patients with risk group II and patients with risk group IV (P < 0.0001). Borderline significant difference was observed between patients with risk group II and patients with risk group III (P = 0.053).

Fig. 2.

Kaplan-Meier analysis of metastasis-free and overall survivals in patients according to TNM stage (A and C) and the QITS (quantitative IMP3 and tumor stage) system (B and D). A, significant difference in metastasis-free survival was observed among three TNM stages (P < 0.0001). For comparisons between each pair of two stages, there is significant difference in metastasis-free survival between patients with stages 1 and 3 (P < 0.0001), and between patients with stages 2 and 3 (P = 0.0001); there is no significant difference in metastasis-free survival between patients with stages 1 and 2 (P = 0.060). B, significant difference in metastasis-free survival was observed among four risk groups of QITS system (P < 0.0001). For comparisons between each pair of two groups, there is significant difference in metastasis-free survival between patients with risk group I and patients with risk group II (P < 0.0001), between patients with risk group I and patients with risk group III (P < 0.0001), between patients with risk group I and patients with risk group IV (P < 0.0001), and between patients with risk group II and patients with risk group IV (P < 0.0001). Borderline significant difference was observed between patients with risk group II and patients with risk group III (P = 0.055). C, significant difference in overall survival was observed among three TNM stages (P < 0.0001). For comparisons between each pair of two stages, there is significant difference in overall survival between patients with stages 1 and 3 (P < 0.0001), and between patients with stages 2 and 3 (P = 0.0001); there is no significant difference in overall survival between patients with stages 1 and 2 (P = 0.441). D, significant difference in overall survival was observed among four risk groups of QITS system (P < 0.0001). For comparisons between each pair of two groups, there is significant difference in overall survival between patients with risk group I and patients with risk group II (P < 0.0001), between patients with risk group I and patients with risk group III (P < 0.0001), between patients with risk group I and patients with risk group IV (P < 0.0001), and between patients with risk group II and patients with risk group IV (P < 0.0001). Borderline significant difference was observed between patients with risk group II and patients with risk group III (P = 0.053).

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Table 3.

QITS and TNM systems with 5- and 10-y metastasis-free survivals

QITS groupsIIIIIIIV
5-y metastasis-free survival 97% 63% 46% 17% 
10-y metastasis-free survival 91% 55% 19% 4% 
     
TNM stage
 
I
 
II
 
III
 
5-y metastasis-free survival 92% 85% 51% 
10-y metastasis-free survival 84% 69% 40% 
QITS groupsIIIIIIIV
5-y metastasis-free survival 97% 63% 46% 17% 
10-y metastasis-free survival 91% 55% 19% 4% 
     
TNM stage
 
I
 
II
 
III
 
5-y metastasis-free survival 92% 85% 51% 
10-y metastasis-free survival 84% 69% 40% 
Table 4.

QITS and TNM systems with 5- and 10-y overall survivals

QITS groupsIIIIIIIV
5-y metastasis-free survival 89% 58% 38% 14% 
10-y metastasis-free survival 72% 41% 17% 4% 
     
TNM stage
 
I
 
II
 
III
 
5-y metastasis-free survival 83% 80% 47% 
10-y metastasis-free survival 67% 58% 30% 
QITS groupsIIIIIIIV
5-y metastasis-free survival 89% 58% 38% 14% 
10-y metastasis-free survival 72% 41% 17% 4% 
     
TNM stage
 
I
 
II
 
III
 
5-y metastasis-free survival 83% 80% 47% 
10-y metastasis-free survival 67% 58% 30% 

The results of the multivariate analysis for metastasis-free survival and overall survival in the 369 patients with localized disease at the time of surgery are presented in Table 5. For these analyses, all factors shown in Table 2 were initially included in the model as potential risk factors. Multivariate Cox proportional hazards regression analysis showed that the QITS system was a strong independent predictor of the patients' clinical outcome. The hazard ratios for metastasis-free survival were 6.85 [95% confidence interval (CI), 3.54-13.25; P < 0.0001] for QITS group I versus QITS group II patients, 11.75 (95% CI, 5.27-26.20; P < 0.0001) for QITS group I versus QITS group III patients, and 20.93 (95% CI, 10.93-43.31; P < 0.0001) for QITS group I versus QITS group IV patients (Table 5). The hazard ratios for overall survival were 2.75 (95% CI, 1.70-4.44; P < 0.0001) for QITS group I versus QITS group II patients, 4.26 (95% CI, 2.39-8.92; P < 0.0001) for QITS group I versus QITS group III patients, and 8.55 (95% CI, 4.86-15.02; P < 0.0001) for QITS group I versus QITS group IV patients (Table 5). These hazard ratios were much higher than the hazard ratios associated with all other independent risk factors (Table 5). In addition to QITS groups, tumor size was also observed as a significant risk factor for metastasis-free survival, and age was also observed as a significant factor for overall survival (Table 5).

Table 5.

Multivariate cox proportional hazard regression analysis for metastasis-free and overall survival

VariableMetastasis-free survival
Overall survival
Hazard ratio (95% CI)PHazard ratio (95% CI)P
QITS group     
    I vs II 6.85 (3.54-13.25) <0.0001 2.75 (1.70-4.44) <0.0001 
    I vs III 11.75 (5.27-26.20) <0.0001 4.26 (2.39-8.92) <0.0001 
    I vs IV 20.93 (10.12-43.31) <0.0001 8.55 (4.86-15.02) <0.0001 
Age 1.00 (0.98-1.02) 0.810 1.02 (1.01-1.04) 0.004 
Sex 1.13 (0.69-1.86) 0.633 1.09 (0.74-1.60) 0.677 
Tumor size 1.06 (1.01-1.12) 0.019 1.02 (0.98-1.07) 0.302 
Tumor grade     
    1 vs 2 1.75 (0.23-13.40) 0.592 0.91 (0.38-2.20) 50.832 
    1 vs 3 4.34 (0.57-32.92) 0.156 1.62 (0.67-3.93) 0.285 
    1 vs 4 3.55 (0.44-28.41) 0.233 1.34 (0.51-3.68) 0.526 
Histological type     
Clear vs papillary 0.48 (0.21-1.07) 0.073 0.69 (0.40-1.22) 0.203 
Clear vs chromophobe 1.14 (0.47-2.75) 0.775 0.94 (0.43-2.07) 0.872 
VariableMetastasis-free survival
Overall survival
Hazard ratio (95% CI)PHazard ratio (95% CI)P
QITS group     
    I vs II 6.85 (3.54-13.25) <0.0001 2.75 (1.70-4.44) <0.0001 
    I vs III 11.75 (5.27-26.20) <0.0001 4.26 (2.39-8.92) <0.0001 
    I vs IV 20.93 (10.12-43.31) <0.0001 8.55 (4.86-15.02) <0.0001 
Age 1.00 (0.98-1.02) 0.810 1.02 (1.01-1.04) 0.004 
Sex 1.13 (0.69-1.86) 0.633 1.09 (0.74-1.60) 0.677 
Tumor size 1.06 (1.01-1.12) 0.019 1.02 (0.98-1.07) 0.302 
Tumor grade     
    1 vs 2 1.75 (0.23-13.40) 0.592 0.91 (0.38-2.20) 50.832 
    1 vs 3 4.34 (0.57-32.92) 0.156 1.62 (0.67-3.93) 0.285 
    1 vs 4 3.55 (0.44-28.41) 0.233 1.34 (0.51-3.68) 0.526 
Histological type     
Clear vs papillary 0.48 (0.21-1.07) 0.073 0.69 (0.40-1.22) 0.203 
Clear vs chromophobe 1.14 (0.47-2.75) 0.775 0.94 (0.43-2.07) 0.872 

In this study, we have shown that the level of IMP3 expression in RCCs, quantitatively determined by a computerized image analyzer (ACIS) when combined with tumor stage, is able to identify patients who have a high potential for the development of metastasis with much higher precision that previous predictive criteria.

The QITS system displays several features that make it useful for determining outcome in patients with localized RCC. First, the QITS system accurately predicts metastasis for patients with localized RCCs. Our data show that almost all group IV patients with localized RCCs developed metastasis after nephrectomy. In the multivariable Cox analysis, patients in group IV developed metastasis at a rate that is 20 times greater than group I patients, after adjusting for other well-known clinical variables. To our knowledge, QITS is the only system that is able to identify a high-risk group of localized RCC patients whose 5-year metastasis-free survival rate is <20% (2730). Our data strongly supports the rationale for trials to determine the benefit of early systematic therapy for group IV patients even without clinical signs of metastasis right after nephrectomy. However, group I patients even with other risk factors, including TNM stage 2 disease, high tumor grade, and clear cell RCC, should not need any further treatment because they have little chance of developing metastasis. As three new drugs, Nexavar (sorafenib), Sutent (sunitinib), and Temsirolimus, have recently shown to be promising treatment for metastatic RCC patients with less toxicity compared with immunotherapy (610), selecting high-risk patients with localized RCCs to undergo systemic therapy after nephrectomy becomes a crucial issue. The QITS system not only provides useful prognostic information for patients with localized RCCs but also more importantly stratifies RCC patients for selecting early systemic adjuvant therapy only for high-risk patients who have an increased potential to develop metastasis.

Second, combining the molecular marker IMP3 with tumor TNM stage would provide important information that identifies high-risk patients in the same TNM stage.

Our data shows that TNM stage 1 and 2 patients with high levels of IMP3 in their tumors (QTIS group IV) have a much higher chance of developing metastasis compared with TNM stage 3 patients without IMP3 expression (QITS group II). In the intermediate risk groups, TNM stage 1 patients with a low level of IMP3 expression (QTIS group III) have a higher chance of developing metastasis compared with TNM stage 3 patients without IMP3 expression (QITS group II). Therefore, our data shows that the combination of IMP3 status with tumor stage system can further stratify patients within the same TNM stage into low- or high-risk groups, and that IMP3 expression can complement the standard TNM staging system.

Third, the QITS system is an easy, simple, inexpensive, and reliable assay that can be standardized across institutions for use in clinical practice. Immunohistochemical staining is widely used in routine clinical practice and is a simple and inexpensive assay. In addition, as localized RCCs are usually treated by partial or radical nephrectomy, tumor tissue is routinely available for immunohistochemical staining. A problem in the analysis of immunohistochemical staining assays is the subjectivity in the interpretation of results and the absence of a uniform definition for positive staining, which could generate an inconsistent outcome (31). In addition, it is impossible to objectively evaluate the levels of protein expression (staining intensity) without an image analysis system. In the QITS system, we used a computerized image analyzer for quantitative immunohistochemistry (ACIS) that is an automated, objective, and quantitative test that previously has been clinically used for the evaluation of Her2/neu gene expression in breast cancer tissue. We have found that the automated image analyzer is not only able to give an objective interpretation of immunohistochemical staining results but also provides important information on the levels of IMP3 expression, which is crucial for predicting metastasis of patients with localized RCC.

Although the QITS system provides significant accuracy for predicting metastasis of localized RCC, further studies to compare the QITS system with current integrated systems for the determination of outcome in RCC are necessary.

In summary, the QITS system by combining quantitative IMP3 expression and tumor staging provides a unique, simple, and accurate approach for the prediction of tumor metastasis. This system will provide important prognostic information for patients with localized RCC and can help physicians select high-risk patients in whom early systematic therapy may be useful.

No potential conflicts of interest were disclosed.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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