Glycogen-Rich Clear Cell Carcinoma of the Breast: Report of Two New Cases and an Updated Literature Review.

[OBJECTIVE] To report two additional cases of glycogen-rich clear cell carcinoma (GRCC) of the breast - detailing their clinicopathologic features, immunophenotypes, and follow-up - and to provide an updated literature review since 2020.

[CASE REPORTS] Two patients (66 and 52 years old) had GRCC confirmed morphologically and histochemically. Case 1 was ER-positive/HER2- positive (luminal B/HER2-positive) and was managed with surgery, followed by adjuvant chemotherapy, endocrine therapy, and anti-HER2 therapy (trastuzumab). Case 2 was triple-negative and received neoadjuvant chemoimmunotherapy (pembrolizumab- based) with marked pathologic tumor regression at resection. Both patients were disease-free at one and 12 months, respectively.

[CONCLUSIONS] GRCC is heterogeneous and should not be regarded as a single clinicopathologic entity within invasive breast carcinoma of no special type or assumed to have a uniform prognosis. Management should be biomarker-guided, as illustrated by these cases. The role of targeted and immune therapies in GRCC warrants multi-institutional studies.