PML‐RARα PCR positivity in the bone marrow of patients with APL precedes haematological relapse by 2–3 months

Summary. We report the results of serial tests in three patients with hyperleucocytotic AML M3 by haematological methods, coagulation assays and PCR analyses following treatment with ATRA and chemotherapy. All three patients became PCR negative in bone marrow and peripheral blood (sensitivity level 1 in 105 cells) after one cycle of ATRA+chemotherapy. However, they relapsed haematologically 6–9 months after achieving complete haematological remission. The haematological relapse was precded by PCR positivity in the bone marrow by 3 months. Platelet counts decreased already during CHR, but dropped below normal levels only at the time of relapse. Coagulation parameters were not helpful for early prediction of relapse. Our results demonstrate that PCR analysis in the bone marrow is the best way to monitor patients with APL. However, in hyperleucocytotic patients, PCR negativity does not seem to indicate long-term remission.