Background: Guidelines for testing human epidermal growth factor receptor 2 (HER2) in breast cancer using fluorescence in situ hybridization (FISH) were released in 2018. These guidelines were jointly developed by the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) to achieve a clearer designation of breast cancer HER2 status. Clinical correlation with other factors was also considered appropriate, especially for those cases classified under ISH groups 2, 3, and 4. Objective: In this study, we examined clinicopathologic features among Filipino breast cancer patients whose HER2 status was reclassified based on the 2018 ASCO/CAP guidelines. Methodology: One hundred and thirty-two (132) breast cancer cases with immunohistochemistry (IHC) equivocal results in the Medical City were enrolled from January 2017 up to December 2020. HER2 FISH results classified under groups 2, 3, and 4 were then re-evaluated for HER2-IHC status in accordance with the 2018 ASCO/CAP guidelines. The relationship between clinicopathologic features and HER2 status was analyzed using the Fisher exact test. Results: Significant differences were found in histologic type, nuclear pleomorphism, mitotic rate, progesterone receptor (PR) status, and regional lymph node involvement among the reclassified ISH groups. In the conv+ group, the tumor cells did not involve the regional lymph nodes as compared to group 5, where the tumor cells were involved. The conv- group had a higher grade for nuclear pleomorphism, mitotic count, and overall Nottingham Histologic Grade than group 5. There was a significant association between progesterone receptors among the conv- group and group 1. Conclusion Filipino breast cancer cases whose HER2 status was reclassified to negative following the 2018 ASCO/CAP guidelines had statistically different clinicopathologic features from those classified as group 5.
Breast Neoplasms ; Immunohistochemistry

This is a case of a 54-year-old, perimenopausal, Asian, woman, who presented with an enlarging left breast mass associated with whitish to bloody nipple discharge. A core needle biopsy, done in another institution, showed histologic findings of a mucinous carcinoma with triple negative “basal-like” biomarker status (ER, PR, HER2/neu). Six cycles of neoadjuvant chemotherapy were given after which the subsequent modified radical mastectomy revealed a centrally located, 10.0 cm, well-circumscribed, nodular, ovoid mass on gross examination. Microscopic findings showed tall columnar cells in stratification, tufts and papillary formations, with surrounding abundant extracellular mucin. The individual tumor cells exhibit enlarged, hyperchromatic, basally located nuclei with prominent nucleoli, abundant amphophilic and occasionally oncocytic cytoplasm which contains intracytoplasmic mucin. Based on the histologic features, “basal-like” biomarker expression, and additional immunohistochemical studies (positive CK7, negative CK20 and CDX2), this case demonstrates a pure mucinous cystadenocarcinoma of the breast. In addition to the rare histologic type, this case is exceptional since, despite multiple cycles of neoadjuvant chemotherapy, presence of extensive lymphovascular invasion and axillary lymph node involvement with extranodal extension remain evident.
Cystadenocarcinoma, Mucinous ; Breast Neoplasms