Hisashi Fukutani

Clonal Analysis of Multiple Point Mutations in the N-ras Gene in Patients with Acute Myeloid Leukemia

We have screened mutations of the N‐ras gene at codons 12, 13, and 61 in leukemia cells obtained from 100 patients with acute myeloid leukemia (AMD, and found mutated N‐ras alleles in 9 patients. We further analyzed the polyclonality of multiple N‐ras gene mutations in 4 AML patients. One patient, who had the monoclonal karyotype, t(11;17), had two types of double missense mutations at codons 13 and 61 in the same allele. Each of the remaining three patients, one of whom had t(15;17) with a monoclonal rearrangement of the retinoic acid receptor alpha and PML genes, carried two missense mutations in a relatively small population of leukemia cells. We have demonstrated that multiple clonality of the N‐ras gene is occasionally observed in leukemia with a monoclonal karyotype. These findings indicate that the N‐ras mutations may not always be characterized simply by an accumulative process and that the activated N‐ras gene alone is not sufficient to cause leukemia.

Molecular Heterogeneity of the PML Gene Rearrangement in Acute Promyelocytic Leukemia: Prevalence and Clinical Significance

We determined the breakpoints of the RAR‐α and PML genes in acute promyelocytic leukemia (APL) cells from 40 patients using Southern blot analysis. We also analyzed the relationship between the location of breakpoints, the clinical features of APL and the response to all‐trans retinoic acid (ATRA). While the breakpoints of the RAR‐α gene were consistently within intron 2, we found two major clusters in the breakpoints of the PML gene. The two breakpoint clusters in the PML gene were separated by 10 kb; 5’breakpoints were in intron 3, and 3’breakpoints were around introns 5 and 6. Twenty percent of the patients had 5’breakpoints in the PML gene and 70% had 3’breakpoints. No rearrangement was observed in the remaining 10% of patients in spite of the presence of t(15;17) translocation. There was no relationship between the location of the PML breakpoints, the clinical features at diagnosis and the response to ATRA.

Effective treatment of adult T cell leukemia/lymphoma with a novel oral antitumor agent, MST-16.

Adult T cell leukemia/lymphoma (ATLL) induced by human T cell leukemia virus I is resistant to conventional therapy. Six patients with ATLL were treated with a new antitumor agent, MST-16, which is a derivative of bis(2,6-dioxopiperazine). Two patients achieved complete remission, lasting 12 months and more than 8 months, and 2 others partial remission, lasting 2 months and 6 weeks, respectively. The major toxicity was myelosuppression. Other toxicities were not severe and were well tolerable. Orally administered MST-16 is a promising agent for the treatment of ATLL.

Final 3-year Results of the Dasatinib Discontinuation Trial in Patients With Chronic Myeloid Leukemia Who Received Dasatinib as a Second-line Treatment

Micro‐Abstract We describe the results of a prospective trial of the discontinuation of second‐line dasatinib treatment in chronic myeloid leukemia patients who maintained a deep molecular response for > 1 year. The treatment‐free remission rate at 36 months was 44.4%. High natural killer cell counts before discontinuation correlated significantly with successful therapy discontinuation. Introduction We previously reported an interim analysis of the DADI (dasatinib discontinuation) trial. The results showed that 48% of patients with chronic myeloid leukemia in the chronic phase who maintained a deep molecular response (DMR) for ≥ 1 year could discontinue second‐ or subsequent‐line dasatinib treatment safely at a median follow‐up of 20 months. However, the results from longer follow‐up periods would be much more useful from a clinical perspective. Patients and Methods The DADI trial was a prospective, multicenter trial conducted in Japan. After confirming a stable DMR for ≥ 1 year, dasatinib treatment subsequent to imatinib or nilotinib was discontinued. After discontinuation, the loss of DMR (even of 1 point) was defined as stringent molecular relapse, thereby triggering therapy resumption. The predictive factors of treatment‐free remission (TFR) were analyzed. Results The median follow‐up period was 44.0 months (interquartile range, 40.5‐48.0 months). The estimated overall TFR rate at 36 months was 44.4% (95% confidence interval, 32.0%‐56.2%). Only 2 patients developed a molecular relapse after the 1‐year cutoff point. The presence of imatinib resistance was a significant risk factor for molecular relapse. Moreover, high natural killer cell and low &ggr;&dgr;+ T‐cell and CD4+ regulatory T‐cell (CD25+CD127low) counts before discontinuation correlated significantly with successful therapy discontinuation. Conclusion These findings suggest that discontinuation of second‐ or subsequent‐line dasatinib after a sustained DMR of ≥ 1 year is feasible, especially for patients with no history of imatinib resistance. In addition, the natural killer cell count was associated with the TFR.