Pseudocellulitis in the Setting of Pemetrexed Treatment for Non-Small Cell Lung Cancer.

Pemetrexed is a chemotherapeutic, antimetabolite agent that has been used in oncology to treat diseases such as metastatic non-small cell lung cancer and unresectable malignant pleural mesothelioma. Pemetrexed use may result in pseudocellulitis, which presents as poorly demarcated patches or plaques with erythema, edema, warmth, and tenderness. These lesions can present unilaterally or bilaterally on the lower extremities. The histologic appearance includes vacuolar interface dermatitis, squamous metaplasia of eccrine coils and ducts, sparse mixed neutrophilic and lymphocytic interstitial inflammatory infiltrate, and widened subcutaneous fibrous septa with cystic fat degeneration. We present the case of a 58-year-old woman with non-small cell lung cancer and pemetrexed-induced pseudocellulitis with distinctive histological features. The clinical appearance of patients with this hypersensitivity condition may mimic cellulitis, emphasizing the importance of increased awareness and consideration of pseudocellulitis in the differential diagnosis of patients on chemotherapy to avoid unnecessary hospitalization and treatment.