Introduction: Despite efforts in advancing early detection programs, 5-20% of breast cancer patients present with distant metastases at diagnosis. Bone is the most frequent site of breast cancer metastasis, noted in 60-80% of metastatic breast cancer (MBC) patients, and is the first site of metastatic disease in 25-40% of patients. The outcome of patients with bone-only MBC (BOM) is usually better than those with visceral metastasis. However, differences between those who present with De-novo BOM and those who progress to bone-only disease following a diagnosis of early stage breast cancer is not clear. Such differences in clinical course might have an implication on aggressiveness of treatment.The aim of the study is to present the clinical and pathological features along with treatment outcomes of breast cancer patients with BOM in relation to timing and type of bone metastasis. Known prognostics factors that affects treatment outcome will be presented.Patients and Methods: Patients with De-novo and those who progressed after an initial diagnosis of early-stage breast cancer with bone-only metastasis diagnosed, treated and followed up at our institution between 2006 and 2018 were included. Data related to characteristic such as, grade, hormonal status, HER-2 status were collected from our electrical medical records, pathology and radiology reports. De-novo BOM was defined as bone metastasis diagnosed at presentation or within the first 4 months of follow up. Results: A total of 242 patients fulfilled our inclusion criteria and were included in the analysis. The median age (range) at diagnosis was 52 (27-80) years. Majority of the patients (77.3%) had De-novo BOM and multiple sites of bone involvement was identified in 82.6%. High- grade (G-III), HER2-positive and hormone receptor (HR)-negative disease were identified in 27.2%, 18.2% and 8.7%, respectively. Majority of the patients were treated with endocrine therapy while 31(12.9%) patients received chemotherapy at presentation.With a median follow up of 37.7 months, 185 (76.4%) of patients progressed, the median time to progression was 17.1 months (range 3-280m). The median overall survival (OS) for patients with de novo BOM disease was significantly shorter than those who developed subsequent bone metastasis; 40.8 months (95% CI, 51.1-184.1) compared to 80.9 months (95% CI, 36.4-47.9), p < 0.001. Tumor grade, HR status and type of bone lesions (lytic or sclerotic) have significant impact on 5-year OS as detailed in Table-1

Conclusions: Bone-only metastasis breast cancer is distinct clinical entity with a favorable prognosis and a prolonged overall survival. Several risk features for poor OS were identified and might be useful tool to design future clinical trials to trigger upscaling endocrine therapy to include newly introduced resistance modulating agents.

Characteristics5-year Progression-Free Survival5-year Overall Survival
PercentageP-valuePercentageP-value
Age (year) <50 22.7 0.55 44.9 0.21 
 ≥50 22.7  39.2  
Tumor grade 27.3 0.005 64.9 0.01 
 II 23.3  43.6  
 III 9.6  26.6  
HER2 Negative 23.1 0.03 43.6 0.79 
 Positive 15.6  32.9  
Estrogen receptors (ER) Negative 16.3 0.15 13.7 0.005 
 Positive 23.1  44.5  
Progesterone receptors (PR) Negative 17.7 0.09 20.6 0.004 
 Positive 23.3  45.5  
Number of bone lesions Multiple 20.6 0.08 39.1 0.08 
 Single 34.5  54.8  
Type of bone metastasis Lytic 28.2 0.93 46.0 0.01 
 Sclerotic 21.5  54.9  
 Mixed 14.6  43.0  
Time of bone metastasis De novo 13.4 <0.001 35.5 <0.001 
 Late 49.0  60.5  
Characteristics5-year Progression-Free Survival5-year Overall Survival
PercentageP-valuePercentageP-value
Age (year) <50 22.7 0.55 44.9 0.21 
 ≥50 22.7  39.2  
Tumor grade 27.3 0.005 64.9 0.01 
 II 23.3  43.6  
 III 9.6  26.6  
HER2 Negative 23.1 0.03 43.6 0.79 
 Positive 15.6  32.9  
Estrogen receptors (ER) Negative 16.3 0.15 13.7 0.005 
 Positive 23.1  44.5  
Progesterone receptors (PR) Negative 17.7 0.09 20.6 0.004 
 Positive 23.3  45.5  
Number of bone lesions Multiple 20.6 0.08 39.1 0.08 
 Single 34.5  54.8  
Type of bone metastasis Lytic 28.2 0.93 46.0 0.01 
 Sclerotic 21.5  54.9  
 Mixed 14.6  43.0  
Time of bone metastasis De novo 13.4 <0.001 35.5 <0.001 
 Late 49.0  60.5  

Citation Format: Lina Marei, Dina Braik, Ayat Taqash, Hikamt Abdel-Razeq. Clinical characteristics, prognostic factors and treatment comes of patients with bone-only metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS14-22.