Invasive lobular carcinoma appearing histiocytoid and difficult to diagnose based on cytology and frozen sections—A case report—

Abstract

Background : Invasive histiocytoid-like lobular carcinoma (HLC) is often misdiagnosed as a benign lesion such as xanthogranuloma or a granular cell tumor. We report a case of invasive HLC in which we compared cytology and frozen section findings.
Case : A woman in her 80s hospitalized for a bilateral breast tumors had the left tumor diagnosed as invasive ductal carcinoma. On cytological examination, the right tumor had cells with plentiful granular cytoplasm and bland nuclei with a few small nucleoli scattered against a clear background. Paraffin-embedded sections showed “Indian-file” invasion patterns and intracytoplasmic lumen unclear in frozen sections. These cells were positive for cytokeratin AE1/3 and cytokeratin 7 and negative for cytokeratin 20, S-100, CD68, and E-cadherin. The definitive tumor diagnosis was HLC. Comparison of xanthogranuloma and granular cell tumors in frozen sections yielded indistinguishable lesions. In cytology, however, xanthogranuloma had an inflammatory background and the granular cell tumor showed extracytoplasmic granules—findings not observed in invasive lobular carcinoma.
Conclusion : The possibility of invasive HLC should be considered when cells with plentiful granular cytoplasm are observed in cytological examination.