Molecular analysis and clinical outcome of adult APL patients with the type V PML-RARα isoform: results from Intergroup protocol 0129

The type V (for variable) promyelocytic leukemia retinoic acid receptor (PML-RAR) transcript, found in approximately 8% of adult patients with acute promyelocytic leukemia (APL), is defined molecularly by truncation of PML exon 6 and frequent insertion of genetic material from RAR intron 2. To more fully characterize the molecular features of PML-RAR V-type transcripts and to determine whether V-form APL patients have a distinct clinical presentation or prognosis, we analyzed 18 adult V-form APL patients enrolled on Intergroup protocol 0129 (INT-0129). Truncations in PML exon 6 ranged from 8 to 146 nucleotides, and 3 to 127 extra nucleotides (1 to 42 extra amino acids) were inserted at the PML exon 6/RAR exon 3 junction in 13 cases. No distinguishing morphologic, cytogenetic, or immunophenotypic features of V-form blasts were identified. A total of 5 of 7 patients induced with ATRA and 8 of 11 patients who received chemotherapy for induction achieved complete remission (CR). Six patients have relapsed, 4 after chemotherapy induction and 2 after ATRA. Nine patients (50%) are alive, 6 in continuous CR, 2 after salvage therapy for relapsed or refractory disease, and 1 after alternative treatment following early removal from protocol. Although the failure rate for V-form APL patients was high (61%), the low power of the current study to detect clinically significant differences precludes a meaningful comparison of clinical outcomes between the 18 V-form cases and non–V-form adult APL patients enrolled on INT-0129.