Bilateral testicular biopsies were performed on 708 males with acute lymphoblastic leukemia completing 24 to 30 months of maintenance chemotherapy in continuous remission. The 73 patients (10.3%) with occult testicular leukemia (TL) had a significantly increased risk of subsequent relapse (P = .0001) and death (P less than .0001) when compared with patients with negative biopsies. Protocol-specified therapy for occult TL included reinduction therapy with concurrent bilateral testicular radiation, and 2 years of maintenance therapy. Four-year event-free survival for patients with negative biopsies was 78.2% +/- 4% versus 65% +/- 14% for patients with occult TL who received protocol-specified therapy (P = .05). This study suggests that (1) occult TL occurs in 10% of males completing 2 years of maintenance therapy; (2) occult TL significantly increases risk for subsequent relapse and death; (3) treatment results for occult TL and isolated overt off therapy TL (no previous biopsy) are similar; and (4) given current therapy, documentation of occult TL after 2 years of therapy does not improve disease-free survival.

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