Thus patients with primary brain tumors are prone to these infections and many centers use prophylactic trimethoprim (80–160 mg orally daily or 160 mg 3 times/week on alternate days)/sulfamethoxazole (800 mg) during radiotherapy (even if the absence of concomitant steroids).118 Alternatively, regular testing of CD4 counts may permit the use of this prophylaxis only when counts drop below 200/μL.118 The discontinuation of prophylaxis is dependent both on the counts and on other parameters such as the use and tapering of steroids. The gene discussed is CD4; the disease is brain neoplasm.