Calcified chondroid mesenchymal neoplasm: a case report of perineal involvement and literature review.

Calcified chondroid mesenchymal neoplasm (CCMN) is a recently characterized solid tumor of bone and soft tissue. Its histological features include the formation of cartilage or chondroid matrix, while molecular characteristics are marked by the presence of FN1 gene rearrangement. This article presents a rare case of CCMN occurring in the perineum of a 59-year-old female. The tumor exhibits the following characteristics: grossly, it appears as a solid nodule; histologically, it demonstrates lobulated growth, with polygonal, oval, or spindle-shaped cells observed within the chondroid matrix, alongside a significant number of osteoclast-like giant cells and calcium phosphate-like deposits. Molecular testing confirmed the presence of an FN1 (exon 36)::FGFR2 (exon 2) gene fusion through RNA sequencing. Immunohistochemical staining did not provide substantial assistance in diagnosing CCMN. Although recurrence occurred post-surgical resection, it was not common. Currently, there are no reported cases of metastasis. Existing literature primarily identifies such tumors in the distal extremities and temporomandibular joint; however, the case reported herein is the first documented occurrence in the perineum of a female. This finding suggests that the spectrum of CCMN may extend beyond the traditionally recognized locations of the distal extremities and temporomandibular joint.