A nipple-like lesion: A case report of leiomyosarcoma on the back

Introduction

Leiomyosarcoma (LMS) of the skin is a rare malignant mesenchymal neoplasm that originates from smooth muscle cells, with an estimated incidence of 0.6 per 1,000,000 person-years in older adults. ¹ Predisposing factors may include precursor leiomyomas, trauma, radiation, chemicals, and sun exposure; however, some patients present without any identifiable risk factor.^2,3 LMS of the skin has a predilection for extensor surfaces of the lower limbs, and may arise in the dermis or subcutaneous tissue, or as metastasis from an internal neoplasm. ⁴ Primary dermal lesions (also known as cutaneous LMS or atypical intradermal smooth muscle neoplasm) ⁵ are confined to the dermis, originate from arrector pili or genital smooth muscles, and more commonly affect men.^6,7 In comparison, subcutaneous LMS lesions extend into the subcutis, equally affect both sexes, originate from vascular smooth muscle cells, and are associated with a higher risk of recurrence and metastasis. ⁷ Despite its malignant nature, the diagnosis of LMS can be extremely challenging since it often presents with non-specific clinical features. Histologically, LMS shares features with other malignant spindle cell tumours; thus, immunohistochemistry is essential to confirm the diagnosis. ⁸ We present the rare case of a primary LMS of the lower back, with unusual nipple-like morphology, in a patient who had another primary LMS on the leg treated over 10 years prior.

Case report

A 74-year-old male presented for an annual skin examination as he had a history of actinic keratoses, basal cell carcinoma, and a remote history of subcutaneous LMS on the left leg over 10 years prior. This LMS had been treated with wide local excision, and neoadjuvant chemotherapy and radiation therapy due to the presence of perineural invasion and many mitotic figures. There had been no recurrence of the LMS, and he was otherwise healthy. On physical examination, an incidental finding of a 5 mm, soft, non-tender, dull reddish-pink dome-shaped papule on an oval, wrinkled (pseudo-crepe-like) pink base was noted on the left lower back (Figure 1). This lesion mimicked an accessory nipple but was in an atypical location. The clinical differential included dermal nevus, neurofibroma, dermatofibroma, and adnexal tumours. A shave biopsy was performed and demonstrated an atypical spindle cell lesion with multiple mitotic figures (Figure 2(a)–(c)). Immunohistochemistry was strongly and diffusely positive for smooth muscle actin (SMA) and desmin (Figure 3). CD10 showed weak focal stromal staining. Cytokeratin 5/6 and P40 were negative. SOX10 stained rare small cells. MelanA was negative. Ki67 showed a proliferation index of 30%. Given his previous history of an LMS at a distinct site (the leg), the favoured diagnosis was a new primary LMS of the lower back. The patient was referred to surgical oncology and was treated with a wide local excision to the fascia. Excisional pathology demonstrated involvement of the dermis and extension into the subcutis. CT scans were negative. Re-excision was performed owing to negative but narrow margins. Because of his history of two distinct primary LMSs, he continues to be followed by surgical oncology with regular CT scans performed as surveillance.

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Figure 1.

(a) & (b) Clinical images of a small reddish-pink papule on a pseudo-crepe-like pink base.

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Figure 2.

(a) 40×; H&E; intersecting bundles and fascicles of spindle-shaped cells with nuclear pleomorphism, cytologic atypia, and nuclear hyperchromasia. (b) 200×; H&E; Predominantly spindle cells with a few fusiform, epithelioid, and anaplastic cells with marked pleomorphism and nuclear hyperchromasia. (c) 400×; H&E; atypical mitotic figures identified.

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Figure 3.

200×; Desmin immunohistochemistry; variable strong cytoplasmic staining.

Discussion

LMS in the skin can manifest in various clinical presentations, including skin-coloured, erythematous, or bluish discrete papules, plaques, or nodules, which may be asymptomatic, tender, or painful.^6,9 The clinical differential is broad and may include benign entities like nevi, neurofibromas, and dermatofibromas. ⁶ Therefore, a high degree of clinical suspicion, especially in at-risk patients, and a biopsy are essential for diagnosis. ⁵ For initial biopsy, inclusion of the subcutaneous plane is needed to identify if there is subcutaneous tumour extension, which would favour a diagnosis of the more aggressive subcutaneous LMS. Because of the overlapping histopathological features of LMS with other spindled cell tumours, immunohistochemistry is required. LMS typically stains positive for desmin, h-caldesmon, and SMA. ⁶ In the present case, diffuse positive SMA and desmin helped to confirm the diagnosis of LMS, with a high Ki-67 proliferation index supporting its malignant nature.

This patient’s presentation is notable for the development of a new primary LMS on the back in the setting of a successfully treated LMS of the left leg over 10 years prior. Given the distinct locations and prior treatment, a metastasis was not favoured. While local recurrences or metastases are well documented for subcutaneous LMS, dermal LMSs are usually solitary, and it is uncommon to develop two non-metastatic subcutaneous LMSs at distinct locations.^1,6,7,9

The standard of care for the treatment of LMS is surgical excision.^6,10 Wide local excision with wide tumour-free margins, including deep fascia for subcutaneous LMS, promotes disease-free survival. ⁶ Mohs micrographic surgery for superficial LMS is gaining favour for its closer margin control, with one systematic review of superficial LMS reporting recurrence rates of 2.08% to 6.25% for Mohs micrographic surgery versus 30% to 50% for wide local excision. ¹⁰ The need for adjuvant therapy, including radiotherapy or, less commonly, chemotherapy, remains unclear and is typically reserved for advanced disease, high-grade, recurrent, or large tumours (>5 cm) or metastases.^6,9

Prognosis depends on lesion location, size, and histological grade.^6,7,9 Currently, there are no universally accepted guidelines for LMS surveillance, with some authors suggesting monitoring with skin checks and/or imaging for at least 5 years after initial diagnosis due to concerns of recurrence or metastasis to the lung, skin, and lymph nodes.^6,9 The present patient’s second LMS was diagnosed as a primary tumour over 10 years after his first LMS, which emphasizes the importance of long-term skin examinations in high-risk individuals. It also highlights the need for ongoing diagnostic vigilance of lesions, even those that are benign appearing, in patients with prior malignancy, especially sarcomas. The involvement of both the dermis and subcutaneous layers in the tumour influences tumour classification and long-term surveillance strategy.^5,9 Further research with larger cutaneous and subcutaneous LMS cohorts over longer-term periods is needed to standardize evidence-based surveillance and treatment strategies for this rare lesion.