Comment
Eccrine porocarcinoma is an exceptionally rare adnexal neoplasm that most commonly affects older adults. The average age at diagnosis is 71 years in men and 75 years in women.2 Our case is rare because of the patient’s age. Benign eccrine poromas occur most frequently on the palms, soles, axillae, and forehead where eccrine density is highest; EPC occurs most frequently on the lower extremities.6 It may arise de novo or from malignant transformation of a preexisting benign poroma. Clinically, EPC may present as an asymptomatic pink-brown papule, plaque, or nodule and may have a polypoid or verrucous appearance, as in our patient. Ulceration is common.7 The differential diagnosis often includes nodular basal cell carcinoma, squamous cell carcinoma, pyogenic granuloma, and seborrheic keratosis.
Histologically, EPCs are characterized by aggregations of cohesive basaloid epithelial cells forming eccrine ductal structures.2 Cellular atypia may be extremely subtle but, if present, can be helpful in differentiating malignant from benign lesions. Features of basal and squamous cell carcinoma also may be present. Definitive diagnosis is frequently based on the overall invasive architectural pattern.5 Robson et al2 examined 69 cases of EPC for high-risk histologic features and concluded that tumor depth greater than 7 mm, mitoses greater than 14 per high-power field, and the presence of lymphovascular invasion were independently predictive of mortality. Moreover, after adjusting for mitosis and depth, an infiltrative border vs a pushing border was strongly predictive of local recurrence.2 Immunohistochemical stains, although not necessary for diagnosis, may have utility as adjunctive tools. Cells lining the ducts within EPCs commonly stain positive for carcinoembryonic antigen, though glandular myoepithelial cells stain positive for S-100. Negative Ber-EP4 staining helps to differentiate EPC from basal cell carcinoma. Abnormal expression of p53 and overexpression of p16 also has been described.4
The rarity of EPC has precluded the development of any evidence-based management guidelines. Historically, the standard of care has been WLE with 2- to 3-cm margins. A review of 105 cases of EPC treated with WLE showed 20% local recurrence, 20% regional metastases, and 12% distant metastasis rates.8 Mohs micrographic surgery, which allows examination of 100% of the surgical margin vs less than 1% for WLE with the standard bread-loafing technique, might be expected to achieve higher cure rates. A review of 29 cases treated with MMS monotherapy demonstrated no local recurrences, distant metastasis, or disease-specific deaths with follow-up ranging from 19 months to 6 years.5 One case was associated with regional lymph node metastases that were treated with completion lymphadenectomy and adjuvant radiation therapy.7 The high mortality rate of patients with nodal disease has led some to recommend PET-CT and SLNB for patients with EPC. However, the prognostic value of such procedures has not been clearly defined and there is no demonstrated survival benefit for treatment of widespread disease. Our patient declined both SLNB and PET-CT, and our plan was to follow him clinically with symptom-directed imaging only.
Conclusion
Patients with EPC generally have a favorable prognosis with prompt diagnosis and complete surgical excision. Although most commonly seen in elderly patients, EPC may present in younger patients and may be clinically and histologically nondescript with little cytologic atypia. Based on a small but growing body of literature, MMS appears to be at least as effective as WLE as a primary treatment modality for EPC, while offering the advantage of tissue sparing in cosmetically or functionally important areas.