Pleomorphic lobular carcinoma in a cat: Clinical, histopathological, and immunohistochemical characterization

Abstract

Mammary carcinomas in cats are highly aggressive neoplasms, often with the development of metastasis. Pleomorphic lobular carcinoma, on the other hand, is an invasive carcinoma with aggressive behavior, rarely diagnosed in humans and dogs. This report describes a case of pleomorphic lobular carcinoma in cats. The histopathological and immunohistochemical features of the neoplasm in this species were characterized. The neoplasm was diagnosed in a 10-year-old cat, with regional lymph node involvement at the time of diagnosis, but without systemic signs based on imaging tests performed prior to mastectomy. However, respiratory clinical signs developed approximately 40 days after surgery, accompanied by neoplastic pleural effusion, and the patient was euthanized due to the onset of neurological signs and poor prognosis. Although uncommon, pleomorphic lobular carcinoma is a neoplasm that can affect cats, and given its poor prognosis, it is important for oncologists and pathologists to be familiar with this entity.

Keywords: breast carcinoma; invasive lobular carcinoma; pleural effusion; stage IV.

Figure 1. Histological features of lobular pleomorphic carcinoma in a cat. A. In the mammary gland and invading the dermis, two neoplastic proliferations were observed: tubulopapillary carcinoma (thick arrow) and lobular pleomorphic carcinoma (thin arrow), with invasive areas in the superficial dermis. B. The lobular pleomorphic carcinoma also exhibited in situ areas (arrow), primarily within the mammary gland, where cells were loosely arranged inside the mammary ducts. C and D. In the invasive areas, cells were arranged in an Indian file pattern or dispersed within the stroma, exhibiting marked pleomorphism, with large nuclei, prominent nucleoli, frequent karyomegaly, bizarre nuclei, and multinucleation.

Figure 2. Immunohistochemical features of lobular pleomorphic carcinoma in a cat. Cells were strongly positive for the progesterone receptor (A) and scored 3 for cyclooxygenase 2 (B). For E-cadherin, the neoplastic cells of the lobular pleomorphic carcinoma were negative (arrow), while the cells of the tubulopapillary carcinoma were positive (asterisk). The Ki67 marker showed positive nuclear staining in approximately 90% of the neoplastic cells (D).