Low-Grade Adenosquamous Carcinoma of the Breast Masquerading as a Fibroepithelial Lesion on Core Biopsy: A Challenging Case.

INTRODUCTION: Diagnosing low-grade adenosquamous carcinoma (LGASC) presents significant challenges due to its subtle morphology, variable immunohistochemical expression, and resemblance to benign lesions like radial scar and complex sclerosing lesions. CASE PRESENTATION: We present a case of a 53-year-old woman with a subareolar mass initially thought to be a fibroepithelial neoplasm on core biopsy. Subsequent wide excision revealed LGASC with oestrogen receptor expression (weak to moderate intensity, 40% of tumour cells). CONCLUSION: These findings, rarely reported, highlight the difficulty of diagnosing LGASC on small tissue samples.

Human epidermal growth factor receptor 2 (HER2) status in breast cancer: practice points and challenges.

Human epidermal growth factor receptor 2 (HER2)-enriched breast cancer benefits significantly from anti-HER2 targeted therapies. This highlights the critical need for precise HER2 immunohistochemistry (IHC) interpretation serving as a triage tool for selecting patients for anti-HER2 regimens. Recently, the emerging eligibility of patients with HER2-low breast cancers for a novel HER2-targeted antibody-drug conjugate (T-DXd) adds challenges to HER2 IHC scoring interpretation, notably in the 0-1+ range, which shows high interobserver and interlaboratory staining platform variability. In this review, we navigate evolving challenges and suggest practical recommendations for HER2 IHC interpretation.

Case report: Metastatic ovarian mucinous carcinoma to the breast: diagnostic challenges and pitfalls.

Metastases to the breast from extramammary sources are extremely rare, with the ovary, primarily high-grade serous carcinoma, being the most common origin. We report a case of breast metastases from advanced stage ovarian mucinous carcinoma in a 48-year-old female- a case hitherto unreported in the literature. The case is noteworthy for its atypical presentation marked by an areolar rash, clinically suggestive of Paget disease of the nipple. This unique clinical scenario, coupled with histopathological examination revealing in-situ-like carcinoma component, posed a diagnostic challenge in discerning the tumour origin. We emphasize the need for heightened awareness among pathologists to avoid misdiagnosing metastatic carcinomas as primary breast tumours, a potential pitfall with significant clinical implications.

HER2-low breast cancers: challenges in the interpretation of immunohistochemistry.

ABSTRACT: Overexpression of human epidermal growth factor receptor 2 (HER2) protein in breast cancers carries significant prognostic and therapeutic implications. Anti-HER2 blockade has shown to be a useful adjunct to surgery in treating HER2-positive tumours. Up till today, the HER2 immunohistochemistry (IHC) and in situ hybridisation (ISH) scoring algorithms are geared towards identifying HER2-positive cases. A recently published Phase III clinical trial (DESTINY-Breast04) has demonstrated that an antibody-drug conjugate (trastuzumab-deruxtecan) significantly reduced disease progression and death in patients with metastatic disease with IHC score 1+ or 2+ and without ISH amplification, defining a new category of cases known as HER2 low. At present, IHC scores 0, 1+ and 2+ show significant interobserver variability, and identifying HER2-low breast cancers may pose significant challenges with the current algorithms. More work is needed in this area to better define HER2-low breast cancers, target the appropriate group of patients and assess treatment efficacy.