Melanoma with cartilaginous differentiation: Diagnostic challenge on fine-needle aspiration with emphasis on differential diagnosis

Fine-needle aspiration (FNA) is a minimally invasive, fast, and accurate diagnostic method for the evaluation of patients with locally recurrent or distant metastases of malignant melanoma. In the vast majority of cases, the diagnosis is straightforward with the characteristic cytologic features well documented in the literature. Divergent differentiation (chondroid, neural, myofibroblastic, and osteocartilagenous) in a melanoma is rare and can potentially create diagnostic challenges if the evaluator is unaware of the same. We report a case of a 46-year-old female with a history of primary anal melanoma who presented with a groin mass. The FNA of the groin mass showed a neoplasm rich in chondroid matrix and raised the possibility of a second primary mesenchymal neoplasm rather than metastasis from the patient's known primary anal melanoma. A review of the histologic features of the anal melanoma showed divergent chondroid differentiation in the anal melanoma with the metastatic deposit in the groin exhibiting extensive chondroid differentiation. The differential diagnostic considerations are discussed.