Beyond the Usual Borders: An Unusual Presentation of Basal Cell Carcinoma in the Axilla

INTRODUCTION

Basal cell carcinoma (BCC) is the most prevalent form of skin cancer, predominantly occurring on sun-exposed regions such as the head and neck.^[1] However, the occurrence of BCC in nonsun-exposed areas, such as the axilla, is exceedingly rare.^[1,2] A retrospective review identified only 70 cases of axillary BCC among 69 patients, indicating a calculated prevalence of merely 0.17%.^[2] These lesions are more commonly observed in Caucasian individuals, with a slight male predominance (male-to-female ratio of 1.2:1) and a modest predilection for the right axilla.^[2]

The pathogenesis of axillary BCC remains poorly understood, particularly in the absence of traditional risk factors such as ultraviolet (UV) radiation exposure, trauma, or chronic immunosuppression.^[3] Histologically, axillary BCCs most commonly present as superficial or nodular subtypes and generally carry an excellent prognosis when treated with complete surgical excision.^[2] Our case demonstrated a nodular subtype with metatypical features, which is a rare histopathological variant.

This report aims to contribute to the limited body of literature on axillary BCC by presenting a new case, highlighting its clinical presentation, histopathological features, and management, to enhance awareness of this uncommon disease entity.

CASE REPORT

A 50-year-old male a businessman by occupation presented with a skin-coloured swelling in the left axilla for two years. Initially, the lesion was grain-sized, then gradually increased to approximately 2 × 2 cm in size. He reported a similar lesion 3 years ago and was treated with radiofrequency ablation. There were no contributory occupational risk factors to this presentation, and no history of similar complaints in the family.

On cutaneous examination, a solitary skin-coloured nodule of 2 × 2 cm size, which was firm in consistency with a central crateriform appearance, was seen [Figure 1]. Differential diagnoses included pyogenic granuloma and dermatofibroma, and the patient was planned for excisional biopsy.

Close

Figure 1: A single skin coloured nodule measuring 2*2 cm was seen on the left axilla (blue arrow).

Export to PPT

Histopathological analysis revealed a malignant neoplasm in the dermis with epidermal attachment. The tumour was composed of atypical basaloid cells arranged in nodules, lobules, and cystic structures embedded within a fibromyxoid stroma. Characteristic features included peripheral palisading of tumour nuclei and the presence of artifactual retraction spaces around tumour nests [Figures 2 and 3]. Tumour cells displayed vesicular chromatin with inconspicuous nucleoli. Additional findings included follicular bulbar differentiation, focal malignant squamoid differentiation, melanin pigmentation, and 2–3 mitoses per 10 HPF (high power fields). These histological features are consistent with pigmented nodular BCC with metatypical features and follicular differentiation. The patient was further referred to the surgery department for a wide local excision.

Close

Figure 2: A malignant infiltrating neoplasm with epidermal attachment composed of atypical basaloid cells arranged in nodules (tumour nest cells), lobules and in cystic pattern separated by fibromyxoid stroma (blue arrow). (Haematoxylin and eosin, 10x).

Export to PPT

Close

Figure 3: Peripheral palisading of basaloid tumour cells with vesicular chromatin and inconspicuous nucleoli (blue arrow). (Haematoxylin and eosin, 40x).

Export to PPT

DISCUSSION

Basal cell carcinoma accounts for about 80% of all nonmelanoma skin cancers.^[4] While the most common sites are those exposed to the sun, finding BCC in areas not usually exposed to sunlight is uncommon. These lesions can be difficult to identify because of their rare site of presentation. In Cohen’s review, axillary BCC showed a slight male predominance and frequent right axilla involvement.^[2] Although UV radiation is the foremost cause of BCC, cases in sun-protected areas like the axilla suggest other possible causes, including long-term irritation, local injury, genetic factors, or immune dysfunction.^[4,5]

Various clinical types of BCC include ulcerative, nodular non-pigmented, nodular, pigmented, superficial, and metatypical (basosquamoid) types, among which Nodular BCC remains the commonest one. Histological variants include nodular, superficial, infiltrative, micronodular, and morpheaform. Nodular BCC is the most common histological variant worldwide, comprising 50–60% of cases.^[2]

Blixt, Nelsen, and Stratman (2013) conducted a study involving 34 patients with 37 histologically aggressive basal cell carcinomas, including infiltrative, desmoplastic, morpheaform, and micronodular subtypes, who were treated with electrodesiccation and curettage (ED&C). Defining recurrence as tumour regrowth within or adjacent to the previous scar, the investigators reported a recurrence rate of 27% after a median follow-up duration of 6.5 years.^[6,7]

In recent years, advancements in basal cell carcinoma (BCC) management have introduced novel therapeutic approaches, particularly for cases unsuitable for surgical excision or radiotherapy. Targeted inhibition of the Hedgehog signalling pathway with agents such as vismodegib and sonidegib has yielded significant clinical responses in locally advanced and metastatic BCC. Nonetheless, treatment durability may be limited by the emergence of resistance and drug-related adverse effects.^[8]

For patients who fail or cannot tolerate these agents, immune checkpoint blockade with anti-PD-1 antibodies like cemiplimab provides an effective alternative, with durable responses reported in phase II trials.^[9] In addition, topical immunomodulators (imiquimod), photodynamic therapy, and intralesional agents remain useful for superficial or low-risk BCC, while electrochemotherapy and oncolytic viral therapies are emerging as promising future approaches.^[9]

Complete surgical excision remains the treatment of choice, offering high cure rates. In high-risk or cosmetically sensitive locations, Mohs micrographic surgery is preferred for its tissue-sparing advantage and lowest recurrence rate.^[2,6]

CONCLUSION

Axillary BCC is exceedingly rare and may be misdiagnosed due to its uncommon site and variable presentation. Clinicians should include BCC in the differential diagnosis of persistent axillary lesions, even in the absence of typical risk factors. Early recognition and complete surgical excision are essential for favourable outcomes.