"Osteoid" Syringoma: A Report of Two Cases of Cutaneous Mixed Tumor With Extensive Ossification and Review of the Literature.

Interestingly, ossification is a rare histopathologic feature in chondroid syringoma, a benign cutaneous adnexal tumor consisting of mixed ductal and chondromyxoid differentiation. We report two cases of chondroid syringoma with pronounced ossification. A 46-year-old Hispanic woman presented with a slowly enlarging, asymptomatic, erythematous nodule on the left upper cutaneous lip abutting the nasal sill. Excisional biopsy revealed a well circumscribed, subcutaneous, biphasic proliferation of ductal epithelial strands and chondromyxoid stroma with prominent trabecular ossification enclosing fatty marrow. The second case was a 76-year-old Native American woman with a progressively growing, erythematous nodule on the posterior neck. Histopathology of the excision demonstrated an encapsulated, subcutaneous, ossified tumor with peripheral eccrine ductal epithelium situated in chondroid matrix with sparse hematopoiesis. The patients exhibited no evidence of recurrence after 2 and 23 months, respectively. To date, nine cases of ossified chondroid syringoma have been published, without evidence of recurrence or malignant transformation. The etiology of osseous metaplasia in chondroid syringomas might occur due to differentiation of pluripotent stem cells. Elevated bone morphogenic protein in modified myoepithelial and stromal cells may be responsible for endochondral osteogenesis in chondroid syringoma. Osseous metaplasia with internal hematopoiesis is also a rare, yet benign finding. Our cases featuring exuberant osseous metaplasia add to the limited reports of this phenomenon co-occurring in patients identifying as Hispanic and Native American. Careful evaluation of cytology and architecture is essential to rule out aggressive mimicking tumors such as atypical or malignant chondroid syringoma, mucinous carcinoma, or metastatic adenocarcinoma with bone invasion.