A 64-year-old man presented with a solitary nodule on his chin that had gradually enlarged over several months. The lesion was firm and nontender and did not feature discharge. The patient did not recall any trauma to the area. He did not have other symptoms or a personal or family history of similar skin conditions or autoimmune diseases.

Physical examination revealed a firm, mobile, nonulcerated subcutaneous mass just left of the midpoint on his chin (Figure 1). It was 4 cm in diameter. No other lesions were noted.

QUESTION

Based on the patient’s history and physical examination, which one of the following is the most likely diagnosis?

• A. Basal cell carcinoma.

• B. Cutaneous large B-cell lymphoma.

• C. Dermatofibroma.

• D. Epidermal inclusion cyst.

• E. Keratoacanthoma.

DISCUSSION

The answer is B: cutaneous large B-cell lymphoma, an extranodal B-cell non-Hodgkin lymphoma that primarily involves the skin without evidence of extracutaneous disease at the time of diagnosis.¹ The etiology is not fully understood; however, it is believed to stem from the clonal proliferation of B cells, genetic abnormalities, chronic inflammation, and immune dysregulation. The condition typically manifests as pruritic, pink to violaceous nodules, plaques, or papules on the scalp, forehead, neck, or trunk. The nodular form progresses slowly with a favorable prognosis, but it has a high rate of recurrence. The diffuse form of cutaneous large B-cell lymphoma has a poor prognosis.²