Imprint Cytology of Tall Cell Carcinoma with Reversed Polarity of the Breast: A Case Report

<b><i>Introduction:</i></b> Tall cell carcinoma with reversed polarity (TCCRP) is a rare histologic subtype of breast cancer that was newly categorized in 2020. TCCRP is a relatively novel tumor, and there are no detailed reports about its cellular morphology. We were able to obtain imprint cytological specimens from fresh TCCRP tissue, and we provide our detailed observations. <b><i>Case Presentation:</i></b> The patient was a 73-year-old Japanese female with a 15-mm mass in her right breast. After invasive breast carcinoma was diagnosed based on a core needle biopsy, a lumpectomy was performed. The pathological examination revealed TCCRP, and Sanger sequencing detected <i>IDH2</i> p.R172M hotspot mutation, which is characteristic of TCCRP. Soon after the surgery, the lumpectomy specimen was sliced before fixation for use in a clinical trial, and imprint cytological materials were obtained from the tumor’s cut surface. Cytologically, the tumor showed papillary-like cell clusters and isolated cells with moderate cellularity. Neoplastic cell aggregates and clusters with thick vascular cores as the axis or with delicate fibrovascular stroma were observed. Most of the neoplastic cells were cuboidal-to-columnar in shape, with mildly to moderately irregularly shaped blunt nuclei. Some intranuclear cytoplasmic inclusions and nuclear grooves were present, resembling the nuclear findings of papillary thyroid carcinoma. The most characteristic finding was the columnar cell clusters with apically located nuclei, giving the impression of reversed polarity. <b><i>Conclusion:</i></b> We described cytological findings in TCCRP, a newly classified rare mammary tumor. Most of the characteristic histologic findings were also observed in imprint cytological specimens. Further studies on practical specimens such as fine-needle aspiration are needed for clinical application.