Pituitary blastoma in a dog: comparative clinical, imaging, and pathologic features of a newly recognized and rare...

Pituitary blastoma (PitB) is an exceedingly rare tumor originating from the anterior pituitary gland, first documented in 2008 in humans. It is considered pathognomonic for DICER1 syndrome, primarily affecting children, although cases in adults have been noted. Clinical manifestations vary widely, attributed to hormone hypersecretion (such as Cushing's syndrome) and mass-related effects (like visual impairment and intracranial pressure changes). Histopathologically, PitB exhibits distinct features: proliferating Rathke's epithelium with rosette formations, adenohypophyseal neuroendocrine cells expressing ACTH and occasionally GH, and primitive small blastemal cells. This report describes the first case of PitB in a dog, presenting with ACTH-dependent hypercortisolism. The canine patient exhibited clinical signs consistent with ACTH-hypersecretion related to a pituitary mass. Histologically, the pituitary mass revealed hallmark features resembling human PitB. Immunohistochemistry confirmed ACTH expression and nuclear expression of TBX19 (TPIT), supporting a corticotroph lineage. CAM 5.2 expression in tubule-forming cells suggested an immature epithelial origin, likely from Rathke's pouch. Although DICER1 mutation analysis was not performed due to technical limitations with FFPE tissue, this case raises the possibility of a similar pathogenetic mechanism in dogs. This canine case expands the known species range of PitB and highlights important clinical, morphological and immunohistochemical parallels with the human counterpart, providing new insights into comparative pituitary tumor pathology.