Abstract P1-03-01: Heterogeneity between core needle biopsy and primary tumor tissue in early breast cancer patients: Comparison of intrinsic subtypes after different treatment regimes

Abstract

Abstract Background: All initial therapeutic decisions in early breast cancer are commonly based on the expression profiles of estrogen (ER), progesterone (PR) and the human epidermal growth factor 2 (HER2) receptors. However, breast cancer is a very heterogeneous disease, and receptor changes were manifold reported during progression. Only little data is known about receptor changes after upfront therapy. Here, we compared receptor expression profiles between core needle biopsy (CNB) tissue and primary tumor tissue after different treatment regimes. Methods: In a German single center study, we retrospectively analyzed 248 breast cancer patients during primary treatment regime between 2014 and 2020. Patients had either neoadjuvant chemotherapy, neoadjuvant endocrine therapy or no upfront therapy. Tumor material was obtained by core needle biopsy (CNB) at primary diagnosis and during primary oncological surgery of the axilla and breast. Analysis of histological subtype, grading, Ki67 index and expression profiling of ER, PR, HER2, was performed using formalin-fixed, paraffin-embedded (FFPE) specimens. Immunohistochemical examination was performed according to the ASCO/CAP guidelines using the Ventana-platform. Tumors were grouped into different intrinsic subtypes according to the international St. Gallen classification in either Luminal A, Luminal B, HER2-enriched or triple negative. 35 patients were excluded because the intrinsic subtype was not specified in the CNB and final postoperative specimen, therefore 213 patients were included in the primary analysis. Results: In the primary analysis (n=213), median age was 53 years (IQR 43 - 64). Based on the initial CNB receptor profile 105 (49%) patients had a Luminal A carcinoma, 46 (22%) patients had a Luminal B HER2 negative carcinoma, 22 (10%) patients had a Luminal B HER2 positive carcinoma, 6 (3%) patients had a HER2 enriched carcinoma and 33 (16%) patients had a triple negative carcinoma. In the primary analysis 84 (39%) patients had neoadjuvant chemotherapy, 48 (23%) patients had neoadjuvant endocrine therapy and 81 (38%) patients had no upfront therapy. Overall, 77 (36%) patients had an intrinsic subtype change between CNB and definitive surgical treatment, 139 (64 %) patients had no subtype change. There were 44 (52%) changes after neoadjuvant chemotherapy, 17 (35%) changes after neoadjuvant endocrine therapy and 16 (20%) subtype changes after no upfront therapy (p<0.0001 for the effect of neoadjuvant chemotherapy). ER receptor status changed in 5 (6%) patients after neoadjuvant chemotherapy, 6 (13%) changes were observed after neoadjuvant endocrine therapy and 2 (2%) ER changes occurred after no upfront therapy. Concerning the PR receptor there were 23 (27%) receptor changes after neoadjuvant chemotherapy, 17 (35%) changes after neoadjuvant endocrine therapy and 9 (11%) changes after no upfront therapy (p<0.0001 for the effect of neoadjuvant endocrine therapy). Regarding the HER2 receptor, there were 18 (21%) receptor status changes after neoadjuvant chemotherapy, 2 (4%) changes after neoadjuvant endocrine therapy and 2 (2%) subtype changes after no upfront therapy (p=0.0001 for the effect of neoadjuvant chemotherapy).Neoadjuvant chemotherapy led significantly more often to a decrease of HER2 expression, compared to neoadjuvant endocrine therapy or no upfront therapy. Conclusions: Our results imply the high frequency of intrinsic subtype changes after neoadjuvant therapy. Subtype changes should be taken into account for an optimal and individual treatment. Further research needs to be conducted to investigate whether an individual treatment decision based on the receptor profile after primary treatment might improve clinical outcome of breast cancer patients. Citation Format: Laura Weydandt, Anne Kreklau, Ivonne Nel, Lars-Christian Horn, Bahriye Aktas. Heterogeneity between core needle biopsy and primary tumor tissue in early breast cancer patients: Comparison of intrinsic subtypes after different treatment regimes [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-03-01.