Eccrine porocarcinoma
Malignant eccrine poroma; porocarcinoma
Eccrine porocarcinoma is the malignant counterpart of the benign eccrine poroma — a sweat-duct adnexal carcinoma typically presenting on the lower limb of an elderly patient as a slowly enlarging plaque, nodule or polypoid lesion that may bleed, ulcerate or itch. A minority arise within a long-standing benign poroma; de novo origin is increasingly recognised in modern series (the "1/3 from poroma" figure derives from older single-institution reports and is probably overstated). The reported regional lymph-node metastasis rate is ~20%, with distant metastasis in ~10%, making it one of the more aggressive sweat-gland tumours. Wide local excision is the mainstay; sentinel-lymph-node biopsy should be considered for high-risk lesions.
Clinical features
- Lower limb (~50%) most common; head, trunk, upper limb less so.
- Median age 65–75; slight female predominance in the largest series (Robson 2001, 40F:29M); sex distribution otherwise variable.
- Slow-growing erythematous, violaceous or pigmented plaque, nodule or polypoid mass.
- Often present for years; abrupt change, bleeding or ulceration in a stable lesion may signal malignant transformation of a benign poroma.
- Risk factors: chronic UV exposure, immunosuppression, prior radiotherapy.
Histology
- Lobules and broad ribbons of poroid (small, monomorphous) and cuticular (larger, eosinophilic) cells extending from the epidermis into the dermis.
- Cytological atypia, increased mitoses (often atypical), tumour necrosis distinguishing it from benign poroma.
- Eccrine ductal differentiation (intracytoplasmic lumina, EMA-positive ducts).
- Adjacent benign poroma may be present in transformed lesions.
- Adverse histological features: high mitotic count (>14/HPF), depth >7 mm, lymphovascular invasion, infiltrative borders.
Management
- Wide local excision with 1–2 cm margins; Mohs micrographic surgery for facial or cosmetically/functionally sensitive sites.
- Imaging staging (CT chest/abdomen/pelvis ± USS regional nodes) for high-risk lesions.
- Sentinel lymph node biopsy considered for tumours >2 cm, high mitotic count, lymphovascular invasion, deep tumours, or recurrent disease.
- Adjuvant radiotherapy for incomplete margins, named-nerve perineural invasion or nodal disease with extracapsular spread.
- Systemic therapy for metastatic disease — limited evidence; platinum-based chemotherapy historically; pembrolizumab has shown activity in small case series.
Prognosis
Local recurrence after WLE 15–20%; regional nodal metastasis ~20%; distant metastasis ~10%. 5-year disease-specific survival 60–80% overall, lower for nodal-positive disease. Long-term surveillance is recommended given delayed recurrence and the elderly comorbid population.
References
- Robson A et al. Eccrine porocarcinoma: a clinicopathologic study of 69 cases. Am J Surg Pathol; 2001.
- Salih AM et al. Porocarcinoma — review. Int J Surg Case Rep; 2017.
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