Management challenges in metachronous bilateral breast cancer with discordant receptor status: a case report

Bilateral breast cancer is uncommon, accounting for 2%-5% of cases, and presents additional clinical challenges when tumors exhibit discordant molecular subtypes. Metachronous tumors, occurring sequentially, require individualized therapeutic strategies, especially when one tumor is triple-negative and the other is hormone-responsive.

We report on a 37-year-old woman who initially presented with a left-sided breast lump during her fifth pregnancy. Histopathology revealed invasive carcinoma of no special type (NST), progesterone receptor (PR)-positive (90%), estrogen receptor (ER)-negative, human epidermal growth factor receptor 2 (HER2)-negative, with a high proliferative index (Ki-67 = 90%), staged T2N2M0 (stage IIB/IIIA). Subsequently, she developed a right-sided breast mass, confirmed as triple-negative invasive carcinoma (T4N3M0, stage IIIC). The patient was initiated on neoadjuvant chemotherapy with the adriamycin and cyclophosphamide (AC) regimen and received supportive care, including ondansetron, morphine, and bisacodyl. Her Eastern Cooperative Oncology Group (ECOG) performance status was 1, and she experienced significant weight loss (from 68 to 46 kg in 4 months). Post-chemotherapy imaging will guide surgical planning.

This case highlights the rarity and complexity of metachronous bilateral breast cancer with discordant receptor status. Therapeutic prioritization is guided by the more aggressive tumor, in this instance, the triple-negative carcinoma, while simultaneously addressing the hormone-responsive lesion. Neoadjuvant chemotherapy allows tumor downstaging, assessment of chemosensitivity, and individualized surgical planning. Multidisciplinary management is essential to optimize outcomes and address prognostic variability between tumors.

Metachronous bilateral breast cancer with discordant molecular subtypes presents significant diagnostic and management challenges. Individualized, biology-driven treatment strategies are critical, emphasizing the importance of systemic therapy guided by the more aggressive tumor and careful post-chemotherapy surgical planning.