Introduction: The pathological complete response (pCR) rate is approaching to 50% particularly in patients with hormone-receptor negative disease by neoadjuvant chemotherapy (NAC). If the disease is not recurred locally in cases with pCR and pCR could be accurately diagnosed preoperatively, it is possible to treat some population of patients without surgery after NAC. We conducted two studies to examine: 1) outcomes of patients who had achieved pCR by NAC with a special attention to local recurrence. 2) diagnostic accuracy of pCR with core needle biopsy (CNB) for cases obtained clinical complete response (cCR) by NAC.

Methods: 1) Clinical outcomes were retrospectively investigated in 395 patients who achieved pCR from 1599 patients with primary operable breast cancer treated by NAC (overall pCR rate of 24.7%: 395/1599). The association of clinic-pathological factors with recurrence was investigated. 2) Ultrasound-guided CNB was performed prospectively for 86 cases who achieved cCR by MRI after NAC. The concordance of pathological results between CNB and surgical specimens was examined. The pathological diagnosis was categorized as no carcinoma (pCR), carcinoma in situ (CIS) and invasive carcinoma (INV).

Results: 1) 395 pCR cases consisted of 50 Luminal type (pCR rate: 7.2%), 98 Luminal-HER2 type (32.1%), 116 HER2 type (52.5%), and 131 triple negative (TN) type (34.2%). The median follow-up was 41 months. Recurrent diseases including local recurrence or distant metastasis were found in 5.80% (23/395). According to subtypes, these were 2.00% (1/50) for Luminal type, 4.08% (4/98) for Luminal-HER2 type, 10.3% (12/116) for HER2 type, and 4.58% (6/131) for TN type. Local recurrence was found in 1.2% of cases (5/395). Risk factors of recurrence were clinical stage before NAC and nodal status after NAC in the univariate analysis, and only clinical stage remained statistically significant in the multivariate analysis. 2) Pathology of surgical specimen revealed pCR in 41 cases (48%), CIS in 17 cases (20%) and INV in 28 cases (32%). Discordant cases: pCR in CNB, but CIS and INV in surgical specimens were found in 24 cases (14 CIS and 10 INV). The false negative rate (FNR) and accuracy of CNB to predict INV were 22.2% and 88.4%, respectively.

Conclusion: Except HER2 type, recurrence was not frequent particularly in cases with an early clinical stage. Local recurrence was rarely observed in any subtype. However, ultrasound-guided CNB for cCR cases diagnosed by MRI was not reliable enough to predict pCR. Thus, imaging diagnosis and biopsy methods need to be improved to achieve 10% of FNR and 90% of accuracy for predicting pCR and to proceed to an observational study without performing surgery.

Citation Format: Takashi Ishikawa, Mariko Asaoka, Kazutaka Narui, Akimitsu Yamada, Nobuyasu Suganuma, Takashi Chishima, Takahiko Kawate, Kana Miyahara, Kazuaki Takabe, Yasushi Ichikawa, Eiichi Sato. Clinical studies to treat without surgery for breast cancer cases who achieved clinical complete response by neoadjuvant chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1601.