Eccrine porocarcinoma (malignant eccrine poroma): A case report
Institute of Pathology, Indian Council of Medical Research, Safdarjang Hospital, New Delhi, India. firstname.lastname@example.org
Eccrine porocarcinoma is a rare malignancy of eccrine sweat gland usually presenting as a long-standing growth on the lower extremity. It is more common in females. It may arise in a pre-existing eccrine poroma. A case presenting as nodular swelling over the dorsum of left hand in a 56-year-old man is described. Cytologic and histologic examination along with flow cytometric analysis is presented.
Eccrine poroma is a benign neoplasm thought to differentiate toward the acrosyringeal portion of the sweat duct . Eccrine porocarcinoma is a rare malignancy of the eccrine sweat gland first described in 1963 by Pinkus and Mehregan . It has a propensity for lower extremity and a female predominance. Some tumors have been reported in continuity with benign pre-existing poroma .
A 56-year-old man presented with a swelling over the dorsum of left hand. The lesion was present for 6 years and had been rapidly growing over the prior 2 months. The patient had a 3 x 3-cm ulcerated nodular growth that was mobile and not fixed to underlying structures. Fine needle aspiration, wedge biopsy, and subsequent excision biopsy were available for study.
Aspiration was performed using a 22 gauge needle and the material so obtained was spread on glass slides and stained with Giemsa. Microscopic examination of the slide showed groups of cells against an inflammatory background. These cells had a very high nuclear:cytoplasmic (N:C) ratio, hyperchromatic nuclei and scanty basophilic cytoplasm (basaloid cells). Cells exhibited marked pleomorphism (Fig. 1). No definitive pattern was observed. The background was inflammatory and not necrotic as one sees in a squamous cell carcinoma. Moreover; individual cells were also not seen. A diagnosis of malignant adnexal tumor was made and excisional biopsy advised.
However in view of the long history, the clinician decided on a wedge biopsy first.
Tissue sent for wedge biopsy was formalin-fixed, paraffin-embedded and 3µm sections were stained with hematoxylin and eosin. The stained sections showed a tumor extending into the dermis from the epidermis and made up of small cuboidal cells (poroid cells) with smooth borders. There were no atypical cells or mitotic activity and a diagnosis of eccrine poroma was made.
Subsequently, patient underwent a wide excision of the growth. The specimen received for histopathology showed a skin-covered nodule measuring 3 x 3-cm with excision margins 2 cm away on all sides. Skin over the swelling was red and ulcerated. Cut section of the tumor revealed a gray-white homogeneous surface. Tissue was processed and H&E sections were studied. The sections showed an ulcerated epidermis with atypical poroid cells extending into the dermis as anastomosing bands and dermal tumor islands. Some tubular structures were seen (Fig. 2). Cells had large and hyperchromatic nuclei. Areas of squamous differentiation mimicking squamous cell carcinoma were also present. Focal necrosis and mitotic activity was also seen.
Flow cytometric analysis of the tissue from excision biopsy reported as a malignant eccrine poroma was done to study the possible prognostic value and revealed an aneuploid population (37.33 %) with an S-phase fraction (SPF) of 30.17 percent on histogram (Fig. 3).
Eccrine porocarcinoma has been reported most frequently in lower extremity (44 %), trunk (24 %) and head (18 %). A few cases have been reported in the upper extremity (8 %) and hand (3 %) . A clinical diagnosis of squamous cell carcinoma was made in our case and FNAC diagnosis of a malignant adnexal tumor conformed to this view of a malignant growth. However, a benign tumor was reported on wedge biopsy and confirmed on review. Excisional biopsy, on the other hand, revealed a malignant tumor. Robson et al. report a benign component in 18 percent of invasive eccrine carcinomas . Orella et al. suggest that as many patients had a long history before diagnosis, maybe this lesion arose in a previously benign eccrine poroma . Our case bears out both possibilities as obviously there was a benign component that was the only part removed during wedge biopsy and the patient had a long (6 year) history. Literature reports of patients having a history of 10, 20, and 27 years are present .
Akalin et al. studied p53 expression in both eccrine poroma and porocarcinoma and concluded that p53 positivity cannot be accepted as a valuable parameter for malignancy because both benign and malignant tumors showed significant p53 protein expression . DNA ploidy status, on the other hand, was shown to be an indicator of malignancy. Flow cytometric analysis of DNA ploidy in benign eccrine poromas found cells of diploid population; malignant tumors showed an aneuploid population in 40 percent cases in a study by Hagler et al. . The aneuploid population of cells on flow cytometric analysis along with an S-phase fraction (SPF) of 30.17 percent in our case indicates an unfavorable prognostic sign. An aneuploid histogram in a tumor usually indicates a bad prognosis but this patient was free of symptoms and recurrences 1½ years after surgery. A study of the cell ploidy in the benign tumor was not available for comparison and the biopsy too small to retrieve material from the paraffin block. This, if available, would have helped in understanding the progress of disease and further management. Though, an aneuploid histogram would indicate a bad prognosis, further studies are necessary on the ploidy status of adnexal tumors, both benign and malignant. DNA ploidy of more cases with a longer followup period will help to understand its value in predicting the prognosis in adnexal tumors.
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