Black Pigmentation on the Tongue Induced by Long-Term Use of Tetracycline Antibiotics in a Colorectal Cancer Patient With Epidermal Growth Factor Receptor (EGFR) Inhibitor-Associated Skin Lesions: A Case Report and Literature Review

Skin lesions are prevalent in patients with metastatic colorectal cancer (mCRC) receiving epidermal growth factor receptor (EGFR) inhibitors, such as panitumumab and cetuximab, often necessitating long-term management. Despite adequate treatment involving topical adrenocorticosteroid medications, severe skin lesions may result in prolonged or discontinued EGFR inhibitor administration. Consequently, tetracycline antibiotics, with their antibacterial and anti-inflammatory effects, are recommended for EGFR inhibitor-induced acne dermatitis. We present a 68-year-old male patient with mCRC who underwent chemotherapy with panitumumab, folinic acid, 5-fluorouracil, and irinotecan but subsequently exhibited black pigmentation on the tongue due to six months of prolonged minocycline administration for treating panitumumab-induced skin lesions. Suspecting minocycline-related adverse effects based on the description and a score of 7 on the Naranjo scale, minocycline was discontinued while other medications were maintained. The color of the dorsal tongue gradually normalized within two weeks after discontinuing minocycline. Presently, chemotherapy is continued, whereas panitumumab is repeatedly started and stopped according to the severity of acneiform efflorescence and paronychia. Panitumumab was continued without dose reduction or discontinuation owing to the suppression of skin lesions by minocycline; however, the patient developed black pigmentation on the tongue accompanied by dysgeusia, negatively affecting the quality of life. Discontinuing minocycline resulted in a gradual improvement of these symptoms. This report underscores the importance of clinicians being vigilant to the risk of black pigmentation on the tongue in patients receiving long-term tetracycline antibiotics for the treatment of EGFR inhibitor-induced skin lesions.