Xeroderma pigmentosum (XP) is recognized by cutaneous photosensitivity to ultraviolet radiation leading to pigmentary changes, photophobia, and tendency to develop malignancies such as squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and melanoma. Spindle Cell Carcinoma (SpCC) is an extremely rare variant of SCC. A case of extremely rare spindle cell squamous cell carcinoma (SpSCC) developing in the setting of XP on the cheek of a 9-year-old boy is presented here.
A 9-year-old boy, known case of XP, presented to the hospital with an erythematous nodule on the cheek [Figure 1] of size 3 × 3 cm. The patient also had multiple brown to black lentigines of size 0.1 × 0.1 cm intermixed with hypopigmented macules of size 0.1 × 0.1 cm to 0.4 × 0.4 cm over photo exposed areas of the face, neck, chest, upper back, bilateral upper and lower limbs, palms, and soles. A provisional diagnosis of BCC was rendered, nodule excised, and sent for histopathological examination. Microscopic sections revealed a biphasic tumor composed of atypical squamous cells with the presence of squamous pearls in the superficial part of the biopsy [Figure 2]. The deeper part of the lesion exhibited spindle cells in fascicles with greater atypia and the presence of atypical mitosis (2–3/10 high power fields) [Figure 3]. The transition from the squamous cell to spindled cell was quite prominent [Figure 4]. No necrosis was noted. On immunohistochemistry (IHC), there was co-expression of cytokeratin (CK) [Figure 5a] and vimentin [Figure 5b]. The tumor cells were negative for S100 and HMB45. A histopathological diagnosis of SpCC was rendered.
The basic defect in XP is the deficient repair of DNA damaged by UV radiation making XP a model disease for sun-induced carcinogenesis. Damaged DNA is removed with the help of NER replaced by new DNA.[3-5] SpCC is a rare poorly differentiated variant of SCC, which portends a worse prognosis compared to the usual SCC. Seen mostly in men in the sixth and seventh decades, it accounts for 1% of all SCCs and mostly is found in the oral cavity, larynx, pharynx. and sinonasal locations. Primary SpSCC of the skin is extremely rare. Exposure to ultraviolet radiation is one of the most important etiological factors in the development of SpSCC. It usually occurs in the backdrop of solar elastosis and lacks keratinization. Exposure to ultraviolet radiation coupled with DNA repair defects possibly made this patient extremely vulnerable to this aggressive neoplasm.
The histological diagnosis is quite challenging. The absence of basaloid cells, peripheral palisading, and retraction clefts excluded BCC. Keratoacanthoma was excluded as there was the absence of a keratin-filled central crater surrounded by the epidermal lip. The presence of invasion into the subcutis, absence of actinic changes, and presence of a connection to the overlying epidermis and positivity for CK ruled out atypical fibroxanthoma. Different theories have been proposed to explain the origin of SpCC. It could possibly arise as a result of dedifferentiation of the spindle cells to the epithelial component. The second theory supports the theory of collision tumors and lastly, some studies report that the spindle component may be a reactive proliferation of the stroma.
Thus, XP is a rare disease and SpSCC developing in its backdrop further makes it challenging to timely diagnose and manage the condition.
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