# Hypercalcemia of malignancy in a dog with cutaneous apocrine gland carcinoma and malignant myoepithelioma

## TL;DR

A dog with a rare skin tumor showed hypercalcemia, which resolved after tumor removal, marking the first case of this condition linked to this tumor type in dogs.

## Contribution

First reported case of hypercalcemia of malignancy associated with apocrine sweat gland carcinoma in dogs.

## Key findings

- The dog had elevated calcium levels linked to a tumor with apocrine gland and myoepithelial components.
- Calcium levels normalized after surgical removal of the tumor.
- Immunohistochemistry confirmed the tumor's dual nature and malignant potential.

## Abstract

Humoral Hypercalcemia of Malignancy (HHM) is a commonly reported condition in dogs affected by several cancers, mostly T-cell lymphoma and anal sac gland carcinomas, but also other type of tumors. We report the case of a 6-years-old, female neutered Border Collie with an ulcered nodule on the right retromandibular region, that had mild serum total calcium elevation (14,1 mg/dl; reference range (RR): 8,4 to 11 mg/dl) in the absence of clinicopathological abnormalities or imaging finding suggesting any known cause of hypercalcemia. Histologically, the tumor had a tubular epithelial component, admixed with a second, dominant, myoepithelial one; immunohistochemically, the former strongly reacted with anti-Cytokeratin antibodies, while the latter had a weak and patchy immunoreactivity both to Cytokeratin and a-SMA, while Vimentin and Calponin immunostaining was strong and diffuse, suggesting the diagnosis of apocrine gland carcinoma and malignant myoepithelioma. After the excision of the tumor, calcium decreased within limits (8.8 mg/dl RR: 8.4 to 11. mg/dl). In the author’s knowledge, this is the first report of HHM associated with apocrine sweat gland carcinoma in the dog.

The online version contains supplementary material available at 10.1007/s11259-025-11011-4.