Abstract 919: Benefit of chemotherapy in early-stage breast cancer with variant histology
Authors: Roy Arya Mariam , Abdullah Syed Maaz , Catalfamo Kayla , Attwood Kristopher , Gandhi Shipra 
Published: April 2023

Abstract
Introduction: Breast cancer (BC) is a heterogenous disease with multiple histological variants (HV) differing in their aggressiveness, survival, and response to treatments. Given the rarity of the HVs, very little is known about their treatment and chemosensitivity. The benefit of chemotherapy (CT) is unclear in hormone receptor-positive HER2 negative (HR+) subtype in the mucinous, medullary, cribriform, and papillary HVs in the NCCN guidelines. We aim to study the benefit of CT in these BC histologies.
Method: We queried the SEER database from 2010-2018 for stage I, II, and III HR+ BC patients (pts) with mucinous, medullary, cribriform, and papillary histologies and examined their overall survival (OS) and disease-specific survival (DSS). Pts with metastatic disease and carcinoma in situ were excluded. The population was divided into two cohorts based on the receipt of adjuvant CT (CT positive (CT+) and CT negative (CT-) groups (gps)). Mann Whitney U and Fisher’s Exact test were used to compare continuous and categorical variables, respectively. Multivariate cox regression models were used for studying the association of CT with OS and DSS, controlling for confounding variables such as surgery, radiation, stage, grade, race, age, sex, and lymph node status. All analyses were conducted in RStudio v4.0.2 at a significance level of 0.05.
Results: In the mucinous histology, out of a total of 11,745 pts, 94% (n= 6,788) were HR+. Among them, 8.5% (n= 580) were CT+ and 91.5% (n= 6208) were CT-. The 5-year (yr) OS was higher for CT+ compared to CT- among all stages (Stage I: 99% vs 92%, HR= 0.12; II: 96% vs 84%, HR= 0.22; III: 94% vs 40%, HR= 0.08, all p&lt;0.001). The benefit of CT in 5-yr DSS was observed only in stage III (96% vs 73%, HR= 0.2, both p&lt;0.001).
In the medullary histology, out of a total of 1,787 pts, 34% (n= 265) were HR+. Among these HR+ BC, all stage III pts received CT and their 5-yr OS was 94%. In stages I and II, CT+ had better 5-yr OS compared to CT- gp, (stage I: 99% vs 90%, p= 0.03, HR= 0.12, p= 0.07; II: 96% vs 91%, p= 0.03, HR= 0.23, p= 0.05). No 5-yr DSS benefit with CT was observed in any stage.
Out of the total 1,110 BC pts with cribriform histology, 93% (n= 617) were HR+. Among them, 13.2% (n= 82) were CT+. The 5-yr OS was higher in CT+ compared to CT- in stage II (98% vs 82%, p=0.02, HR= 0.2, p= 0.036), but not in stage I or III. 5-yr DSS was not significantly better with CT in any stage.
In the papillary histology, out of the total 1,698 pts, 83% (n= 889) were HR+. Among them, CT+ had better 5-yr OS compared to CT- only in stage II (86% vs 78%, p= 0.04, HR= 0.46, p= 0.047). There was no statistically significant DSS benefit with CT at any stage.
Conclusion: In this large retrospective study, we observed that in mucinous and medullary histologies, adjuvant CT has OS benefit in HR+ BC subtype. In HR+ papillary and cribriform histologies, CT can be considered in higher stages. Multicenter clinical trials would be beneficial to assess the impact of CT in HVs and to formulate guidelines.
Citation Format: Arya Mariam Roy, Syed Maaz Abdullah, Kayla Catalfamo, Kristopher Attwood, Shipra Gandhi. Benefit of chemotherapy in early-stage breast cancer with variant histology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 919.