Frank Invasion in Tall Cell Carcinoma With Reversed Polarity of the Breast: Report of Two Cases

Tall cell carcinoma with reversed polarity (TCCRP) is a rare neoplasm of the breast composed of columnar tumor cells arranged in solid and solid-papillary nests with evidence of apical nuclear polarity. No frank invasion is evident despite the lack of a myoepithelial cell layer throughout the tumor. TCCRP has a triple-negative or hormone receptor-low immunophenotype. Recurrent IDH2 R172 hotspot mutation coexisting with genetic alterations in the PI3K pathway characterizes this tumor. Here, we report on 2 postmenopausal patients with TCCRP with frank stromal invasion. IDH2 R172 mutations were detected in both tumors by immunohistochemistry. Targeted sequencing of case 2 demonstrated the presence of IDH2 R172T and RTEL1 E839K mutations. Both patients underwent breast conservation surgery, radiation therapy, and adjuvant endocrine therapy with anastrozole and demonstrated no evidence of disease at 65 and 25 months, respectively. This study suggests that TCCRP may give rise to frank invasive carcinoma, the prognostic significance of which is yet unknown.