A patient with a history of organ transplant (allograft) presents with oral tongue lesions. What is the most likely cause?

Organ transplant recipients require long-term immunosuppressive therapy (e.g., cyclosporine, tacrolimus, azathioprine, corticosteroids, mycophenolate). These drugs have numerous oral side effects: cyclosporine causes gingival overgrowth in 30-50% of patients; corticosteroids predispose to oral candidiasis; and various agents cause lichenoid reactions, mucositis, or ulcerations. Oral tongue lesions in a transplant patient are most likely medication-related. Opportunistic infections (option c, such as CMV or HSV reactivation) are also possible in immunosuppressed patients but are less common as a first consideration compared to direct drug side effects.