Eccrine porocarcinoma (malignant eccrine poroma) - A clinicopathologic study of 69 cases

The clinicopathologic characteristics of 69 cases of eccrine porocarcinoma (EP) have been studied. Seven cases of purely in situ disease are included. Forty patients were female, 29 male with ages ranging from 29 to 91 years (mean 73 years). The lower extremity represented the single most common sit e (44%). Other common sites were the trunk (15 cases, 24%) and head (11 cas es, 18%). The histologic diagnosis of EP was predicated on the basis of an irregular tumor at least partly formed of characteristic poromatous basaloi d epithelial cells displaying ductal differentiation, and significant cytol ogic atypia. Forty-seven tumors (68%) contained mature well-formed eccrine ducts having an eosinophilic luminal cuticle, with the remaining tumors con taining small ill-formed ducts and/or intracytoplasmic lumina. All ducts we re discernible via light microscopy and in 49 cases were highlighted with D PAS stain and/or CEA/EMA immunocytochemistry. A variant with a broad pushin g tumor margin and marked nuclear pleomorphism showed some resemblance to p roliferative bowenoid dysplasia. In 11 cases (18%) the tumors appeared to a rise in continuity with a benign preexistent poroma. A variety of histologi c patterns were displayed including clear, squamous, and spindle cell diffe rentiation, mucus cell metaplasia, and colonization by melanocytes. Lymphov ascular invasion was present in 9 cases (15%). Three cases showed pagetoid extension of malignant cells (epidermotropism) and appeared to be multifoca l. Follow-up was available in 54 patients (78%) with 9 (17%) experiencing l ocal recurrence, 10 developing lymph node metastases (19%), and 6 (11%) exp eriencing distant metastases or death. Mitoses, the presence of lymphovascu lar invasion, and tumor depth >7 mm were associated with a poorer prognosis . Dividing tumors into those with a "pushing" or "infiltrating" advancing m argin was also predictive of outcome with the latter having an increased ri sk of local recurrence. This report, the largest series of EP to date, sugg ests that the incidence of aggressive behavior is less than popularly belie ved. Furthermore, EP can display a wide variety of histologic patterns that may lead to diagnostic error in the unwary. The large number of cases in t his series enables a reliable evaluation of prognostic parameters. A more a ggressive clinical course may be indicated by more than 14 mitoses per high power field (hazard ratio [HR] for death 17.0, 95% confidence interval [CI ] 2.71-107), lymphovascular invasion by tumor (IIR 4.41, CI 1.13-17.2), and depth >7 mm (HR 5.49, CI 1.0-30.3). Thus, mitoses, lymphovascular invasion , and tumor depth should be evaluated in these tumors. We also suggest that tumors presenting an "infiltrative" advancing margin are particularly pron e to local recurrence and require wide excision with close attention to the surgical margins by the reporting pathologist.