Hidradenocarcinoma: A Rare Sweat Gland Neoplasm Presenting as Small Turban Tumor of the Scalp.

Hidradenocarcinomas are very rare malignant sweat gland tumors that possess an infiltrative and/or low metastatic potential. Here we describe an interesting case of hidradenoma on the fronto-parietal region of the scalp of an elderly female, part of which had developed carcinomatous changes, infiltrating up to the pericranium. She developed intense itching, pain, spontaneous ulceration and rapid increase in the size of the tumor correlating with the expression of malignant behavior of the neoplasm. An initial incision biopsy suggested features of benign poroid hidradenoma, while the histology from the excised tumor exhibited a fairly well circumscribed epithelial neoplasm in dermis consisting of interconnected nodules as well as differentiated ducts, the neoplastic cells showing mild pleomorphism of nuclei, mitotic figures and abundant pale cytoplasm. Clefts, sclerotic stroma and foci of necrosis en mass were also seen. The final diagnosis was a well differentiated and slow growing hidradenocarcinoma. The tumor recurred locally despite total excision.

What was known?

Hidradenocarcinoma is a rare sweat gland tumor presenting as subcutaneous nodules and usually having a low malignant potential. Histologically, it shows uncircumscribed tumor with varying degrees of differentiation of cells along the sweat ducts, necrosis, increased mitoses, dysplasia, perineural invasion and nuclear-cytoplasmic ratio. Usually it is cured by wide excision.

Introduction

Sweat gland tumors are exceedingly uncommon, hidradenocarcinomas are even rarer intradermal malignant sweat gland tumors that present as asymptomatic nodules on skin, which possess an infiltrative and/or low (approximately 6%) metastatic potential.[1] We describe below a rare case of poroid hidradenoma on the frontoparietal region of the scalp, part of which had developed carcinomatous changes, infiltrating up to the pericranium.

Case Report

A 50-year-old female patient presented with an indolent cutaneous nodule growing at the frontoparietal region of anterior scalp since last 6 years. It was asymptomatic to begin with, but started producing intense itch since last 4 years, later associated with intermittent localized pain and scanty purulent discharge from an erosion spontaneously formed on the nodule since last 1 year. There was no history of any local trauma or bleeding from the growth. The personal and family medical history were insignificant especially pertaining to any malignancies, immunosuppression or related symptoms. A thorough systemic and general physical examination did not reveal any significant clinical abnormality or any local or distant lymphadenopathy. The local examination displayed a dull erythematous, woody firm, non-tender, non-fluctuant, multinodular, cauliflower-shaped growth of size 7 × 7 cm which was fixed to the deeper subcutaneous tissues at mid frontoparietal region of scalp. The overlying skin was tense, smooth and eroded at the center with superficial crust deposition. Overall, it appeared like a small turban tumor clinically [Figure 1]. X-ray skull and CT scan showed a lobular supratentorial lesion within the scalp in the midline showing nodular foci of calcification and necrotic component. There was outer table bony erosion but no intracranial extension. The clinical differentials included cylindroma (the archetypal turban tumor), dermatofibrosarcoma protuberans, cutaneous metastases (from occult primary) and deep fungal infection. An initial incisional biopsy suggested a diagnosis of an epithelial neoplasm, made up of numerous rounded tumor islands composed of small and dark poroid cells and large pink cuticular cells. Both types of cells were somewhat monomorphous cells with rounded nuclei although occasional mitotic figures were also present. A few ducts and occasional necrotic areas could also be seen within the tumor islands. The stroma showed abundant fibroplasia, clefts and dilated capillaries. Overall features were consistent with a benign tumor, but with atypical features. The morphology of cells and necrosis pointed towards poroma, however, the architecture and dermal localization of the neoplasm were features in favor of hidradenoma [Figure 2a and b]. The closest acceptable fit was a mix/overlap diagnosis of atypical poroid hidradenoma. We planned a wide local excision, which was performed under local anesthesia. The outer table of skull had to be chiseled out [Figure 3] and the resultant defect had to be covered with flap advancement and a split-thickness skin graft, which healed slowly in about 6 weeks. A biopsy of the excised tumor exhibited a fairly well circumscribed epithelial neoplasm with no connection with overlying epidermis. It consisted of interconnected nodules as well as differentiated ducts, the neoplastic cells showing pleomorphism of nuclei with occasional normal and abnormal mitotic figures and abundant pale cytoplasm. Foci of en masse necrosis and clefts separating the tumor cells from the surrounding sclerotic stroma were also present. These features were consistent with a well circumscribed and slowly growing hidradenocarcinoma [Figure 4a-c]. It is probable that malignancy originated within the mass of benign hidradenoma that had been present since many years. Surgical margins and base were free of tumor. The patient was following in the outpatient clinic with apparent complete healing of the surgical wound after 3 months. However, at the last visit (6 months post-operative) the patient presented with a local recurrence in form of large multinodular tumor at the same site.

Figure 1

Multinodular swelling mimicking small turban tumor

Figure 2

(a and b) Poroid hidradenoma in initial incisional biopsy

Figure 3

Excised tumor (intraoperative)

Figure 4

(a-c) Malignant hidradenocarcinoma with ductal differentiation

Discussion

Hidradenocarcinoma is an exceptionally uncommon adnexal malignancy of either eccrine or apocrine origin. It presents as asymptomatic, well-circumscribed nodular cutaneous lesions in elderly females with infiltrative and/or low metastatic potential. Clear cell hidradenocarcinomas are most common in the head and neck regions and eyelids. There are no precise clinical features differentiating the tumor from other adnexal neoplasms.[2] The clinical differentials include lipomas, hemangiomas, malignant melanoma, dermatofibrosarcoma, other adnexal neoplasms like poroma, cylindroma, and metastatic tumors to the skin. Hidradenomas are characterized by nests, ductular lumens and nodules of monomorphous polyhedral neoplastic epithelial cells in the dermis, the cells have morphological similarity with those of acrospiromas, which include poromas, dermal duct tumors, clear cell hidradenomas and hidroacanthoma simplex.[3] Histology of hidradenocarcinoma shows ductal structures, intracytoplasmic tubular vacuoles, areas of invasion and tumor necrosis. Pleomorphism, cytonuclear atypia and increased mitotic activity, in addition to uncircumscribed tumor with infiltrative borders, vascular and neural invasion and lymph node metastases may help distinguish it from hidradenoma.[345] Its behavior ranges from locally recurring, low grade well differentiated tumor to highly aggressive high grade tumor with potential for local and distant metastasis to lymph nodes, bones and lungs with poor prognosis.[34]

Most cutaneous adnexal tumors are not common enough to be readily diagnosed by dermatologists. The multinodular erythematous growth on the scalp of our patient clinically mimicked a small “turban tumor”, which is classically almost synonymous with cylindroma, in which the tumefaction extensively wraps the scalp. The initial incisional biopsy narrowed down the differentials to adnexal tumors of sudoriferous origin. The cells were poroid in morphology with ductal differentiation, but the tumor was localized to the dermis. Some dysplastic features like few mitotic figures and necrotic areas were also remarkable, suggesting an atypical rather than completely benign lesion. The “second look” inside the tumor after excision disclosed the hidden carcinomatous changes within the atypical neoplasm. This type of mix between poroma and hidradenoma is not unforeseen however, and the lucidity of categorization is often compromised in these tumors exhibiting elements of mixed differentiation.[6] Even after blending the data obtained from histology, electron microscopy and immunohistochemical analyses (namely, P53 protein expression study, expression of angiotensin type 1 receptors and expression of CEA), dissonant opinions persist regarding the specific cell of origin in many cases. Pluripotency of the undifferentiated tumor cells may be able to somewhat explain these disparities.[7] We could not perform specific immunohistochemical analyses due to unavailability of the stains.

Although limited treatment strategies exist, detailed data including TNM staging, histologic type and grade, location and patient's age should be assembled together for optimal treatment strategy.[8] The standard primary treatment is wide local excision or Mohs micrographic excision with or without regional lymphadenectomy. Alternative approaches like radiotherapy alone or concomitant electrochemotherapy and radiotherapy have also been successful. Metastatic lesions can be treated with chemotherapy. Sunitinib, an oral tyrosine kinase inhibitor has also been successfully tried for metastatic neoplasms.[8]

Conclusion

There were clinically and histologically interesting observations in this patient. An unusual multinodular morphology was accompanied by co-existing poroid and hidradenoma cells. Possibly hidradenocarcinoma originated within the nest of benign or atypical tumor cells.

What is new?

The large multinodular swelling mimicked a small turban tumor clinically, unusual for these type of tumors.

The incisional and excisional biopsy features differed, which along with the typical changing clinical features suggested evolution of the malignancy from initial atypical tumor.

Histology from the incisional biopsy revealed very interesting features in form of overlap between poroma and hidradenoma, which might be thought as another extremely rare entity called as poroid hidradenoma.