Abstract P6-01-30: PgR levels and Ki67 expression of Lobular Carcinomas of the Breast might indicate OncotypeDX testing to evaluate Chemotherapy benefit

Abstract

Abstract AIM: The majority of invasive lobular carcinomas (ILC) of the breast are luminal A tumors of good prognosis, having a low or intermediate OncotypeDX Recurrence Score (RS). They are usually treated with hormonal therapy only and some have doubted the relevance of the RS for patients with ILC. However, in a number of ILC cases a high RS can be found, indicating chemotherapy benefit. The aim of the present analysis was to explore in our database of lobular carcinomas analyzed with OncotypeDX, the percentage of tumors with a RS >25 and test the hypothesis if Progesterone Receptor (PgR) and/or Ki-67 expression could be an indicator to have patients evaluated with OncotypeDX. PATIENTS AND METHODS: Among 2.946 patients analyzed with Oncotype DX, we found 397 patients with pure lobular carcinomas (13.47%). Ki-67 expression was obtained from 315 patients and 13 of them (4%) had a high Ki-67 value of >30%. PgR expression was negative in 56 out of 397 patients (14%). We analyzed the possible relationship of RS values with PgR levels and Ki-67 expression. RESULTS: Overall, 94% of patients with ILC had a Recurrence Score ≤25 and only 6% (24/397) had a RS ≥26. There was a wide distribution of RS among patients with different values of PgR; however, there was a negative trend of Recurrence Score values and PgR expression levels. This trend was more obvious in the 56 patients with negative PgR expression. Although there were high RS values across all levels of Ki-67 expression, there was a trend towards high RS with higher Ki-67 expression; 5 out of 13 patients (38%) with ki-67 >30% had a RS ≥26. CONCLUSION: Our analysis shows that the majority of lobular carcinomas of the breast have a low OncotypeDX RS, suggesting that can be treated only with hormonal therapy. However, negative or low PgR levels and high Ki-67 expression might predict a high RS and thus chemotherapy benefit and those two parameters could be used as indicators for OncotypeDX evaluation of lobular carcinomas of the breast. Citation Format: Christos Markopoulos, Mahi Sariyanni, Asimina Karamargiou, Zoi Antonopoulou, Nikolaos Tsoulos. PgR levels and Ki67 expression of Lobular Carcinomas of the Breast might indicate OncotypeDX testing to evaluate Chemotherapy benefit [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-30.