Immunohistochemical diagnosis of invasive dedifferentiated malignant melanoma in a red ruffed lemur ( Varecia rubra )

Abstract This case report details the presentation, diagnosis and treatment of a malignant melanoma in a red ruffed lemur ( Varecia rubra ) and its subsequent recurrence in a dedifferentiated form. The 24‐year‐old male red ruffed lemur presented initially for excision of a cutaneous mass overlying the dorsal left scapula, which had proved refractory to a short course of medical treatment. Surgical intervention was routine, and the individual was observed to make a full recovery. However, malignant melanoma recurred approximately five months later in a markedly morphologically distinct phenotype displaying a high degree of immunohistochemical dedifferentiation. Further surgical intervention was not feasible due to the aggressive nature of the recurrent neoplasm, and the individual was subsequently euthanased. Comparison of postmortem immunohistochemistry performed on the initial and recurrent lesions demonstrated their common cellular origin, confirming a recurrence of the original malignant melanoma in a dedifferentiated form.