Pilomatrix carcinoma
Pilomatrical carcinoma; matrical carcinoma; malignant calcifying epithelioma
Pilomatrix carcinoma is the rare malignant counterpart of pilomatrixoma (calcifying epithelioma of Malherbe), a follicular adnexal tumour with differentiation toward the matrical epithelium of the hair bulb. It typically presents on the head, neck, scalp or upper back of older adults as a firm dermal/subcutaneous nodule that may be larger, faster-growing, or recurrent compared with the benign counterpart, often with ulceration and induration. Both benign and malignant variants share CTNNB1 (β-catenin) pathway activation, but pilomatrix carcinoma demonstrates unequivocal cytological atypia, infiltrative growth, mitoses, lymphovascular invasion and a metastatic risk of ~10–20%. Wide local excision is the treatment of choice; sentinel lymph node biopsy and adjuvant radiotherapy are considered for high-risk disease.
Clinical features
- Firm, slowly to rapidly growing dermal/subcutaneous nodule; may ulcerate or fix to deeper structures.
- Most common on the head and neck, scalp and upper back; M>F (~2:1); median age 60.
- Often arises de novo; less commonly from a pre-existing pilomatrixoma.
- Differential: pilomatrixoma (benign), epidermal cyst, BCC, atypical fibroxanthoma, cutaneous metastasis.
Histology
- Sheets of basaloid matrical-type cells transitioning into eosinophilic ghost (shadow) cells with lost nuclei but preserved cellular outlines — characteristic of matrical differentiation.
- Calcification frequently present.
- Cytological atypia, brisk mitoses (often atypical), tumour necrosis and infiltrative borders distinguish carcinoma from benign pilomatrixoma.
- Lymphovascular and perineural invasion may be present in high-risk lesions.
- Immunohistochemistry: nuclear β-catenin (CTNNB1) accumulation; CK5/6+, CK14+, BerEP4+; lacks p63 in shadow-cell areas.
- Differential by histology: matrical SCC, basal cell carcinoma with matrical differentiation.
Management
- Wide local excision with at least 1 cm margins; Mohs micrographic surgery for facial / scalp lesions where tissue conservation is important.
- Sentinel lymph node biopsy considered for tumours >2 cm, lymphovascular invasion or recurrence.
- Adjuvant radiotherapy for incomplete margins, multiple positive nodes or extracapsular spread.
- Imaging staging (CT chest/abdomen/pelvis) in high-risk cases.
- Systemic therapy for metastatic disease — limited evidence; case reports of platinum-based chemotherapy and immune checkpoint inhibitor activity.
Prognosis
Local recurrence 50–60% with conservative excision; lower with wide excision or Mohs. Regional or distant metastasis (lung, bone) ~10–20%. 5-year overall survival ~70%. Long-term surveillance is essential — recurrence may occur late.
References
- Hardisson D et al. Pilomatrix carcinoma — clinicopathologic study. Am J Dermatopathol; 2001.
- Niedermeyer HP et al. Pilomatrix carcinoma — review. Eur J Surg Oncol; 1996.
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