Discussion
EPC is a potentially lethal neoplasm. It was previously known as eccrine adenocarcinoma or malignant eccrine poroma.6 The origin of this tumor is from the intraepidermal and dermal eccrine ducts.
Some etiological factors for EPC are radiotherapy, ultraviolet radiation and immunosuppression with unknown pathogenesis.4 None of these risk factors were present in our case. It is postulated that the upper portion of the dermal eccrine duct could have a role in the oncogenesis. The p53 gene involved in tumor suppressing could be involved in EPC carcinogenesis.1
The clinical differential diagnoses include cutaneous squamous cell carcinoma (SCC), cutaneous lymphoma, extramammary paget’s disease, bowen’s disease, cutaneous metastasis, amelanotic melanoma, or other primary skin appendageal tumors.6 Diagnosis of EPC is difficult because of variable presentations and similar clinical and histological features to cutaneous SCC,5 which was differentiated by the presence of cuticles and positivity for EMA in our case.
Mature duct formation, identified as the presence of ducts lined by cuboidal epithelial cells commonly with an eosinophilic cuticle, was found in 62%∼68% in previous studies.7 This characteristic cuticle formation were also prominent in our case that demonstrated EMA positivity in rim of ductules. (Fig 2F)
Histopathologically, factors associated with worse prognosis are mitotic index >14/high power field (hpf), lymphovascular invasion and tumor depth ≥7mm. Clinically, few factors which yield poor prognosis are associated with local recurrences, regional lymph node and distant metastases.8
Our case had ~20 mitosis/hpf, showed lymphovascular invasion with ipsilateral axillary nodal metastasis and a tumor depth of 4cm all of which fares a poorer prognosis.