Treatment Results and Malignant Complications in Patients on Long-Term Treatment with Tyrosine Kinase Inhibitors(TKIs) for Chronic Myeloid Leukemia(CML)

With the introduction of imatinib (IM) and subsequent TKIs such as nilotinib (NI) and dasatinib (DA), deaths due to progression of chronic myeloid leukemia (CML) have decreased dramatically. In such circumstances, the new occurrence of other malignant diseases in patients with CML on treatment with TKIs always causes distress. With the increase in long term surviving patients with CML, there is concern over whether these malignancies are related to treatment with TKIs or not. We investigated the improved prognosis in patients with CML on long-term treatment with TKIs and the occurrence of complicating malignancies.

We evaluated 173 patients (101 males, 72 females) in the chronic phase of CML, all of whom had CML diagnosed at our hospital between January 1990 and June 2011 and received treatment with TKIs for at least 1 year. The median age at the start of treatment with TKIs was 57 (19 – 92) years. Patients aged 60 years and older accounted for 72 (42%). The median follow-up period after the start of treatment with TKIs was 68 (12 – 128) months. Before the onset of CML, 11 patients had prior malignancies. Treatments for CML administered before use of TKIs were hydroxyurea (HU) alone 3, HU + interferon-α (IFN-α) 47, IFN-α alone 7, chemotherapy for AML + IFN-α 2 and chemotherapy for ML + IFN-α 1. TKIs were used as frontline therapy in 113.TKI treatment of all patients initially consisted of IM at the dose of 100 mg per 12 kg body weight. We switched the drug to NI when complete molecular response (CMR) was not achieved after long-term treatment with IM. In addition, a switch to DA was used to consolidate CMR. Treatments that contained TKIs consisted of IM alone in 42, IM → NI in 46, and IM →NI → DA in 85. Two patients with a complete cytogenetic response (CCR) underwent bone marrow transplantation.

Among 173 patients, the best response to treatment in patients treated with TKIs was CMR in 72, a major molecular response (MMR) in 84, CCR in 15, and refractory CML in 2. Currently, 22 have maintained CMR for 6 to 111 months after discontinuation of TKIs, and 19 (11%; 17 males, 2 females) have developed new onset of a malignancy. In these 19, the median age at the onset of cancer was 70 (31 – 85) years. Patients aged 60 years and older accounted for 15 (79%). The median period from the start of TKIs to the onset of cancer was 38 (10 – 117) months. Affected organs were bladder 5; stomach 3; rectum 3; large intestine 2; lung 2; and esophagus, appendix, prostate, and pancreas each in 1. The TKIs given to the patients with malignant diseases were IM alone in 13, IM → NI in 4, and IM → NI → DA in 2. Prior treatments included HU + IFN-α in 8 and IFN-α alone in 1. The observed number of patients who were diagnosed as malignant neoplasm was compared with the expected number. The expected number was obtained through integration of age specific incidence rate of malignant neoplasm from the start age taking medicine to the age at which the diagnosis as malignancy was made or the follow up was finished for censoring. The age specific incidence rates were estimated by interpolating five year old specific incidence rates from of the 2007's survey that was conducted by Center for Cancer Control and Information Services, National Cancer Center, Japan. The observed number/expected number (O/E) ratio for the occurrence of all malignant diseases was 1.00 (19/18.97), and the O/E for gastrointestinal cancer was 1.118 (11/9.84). Therefore, no increase in the incidence of malignant diseases was observed in patients treated with TKIs. However, the O/E for bladder cancer was 4.525 (5/1.11) with a 95% confidence interval of 1.42 – 9.32 (P = 0.0002), which means that the incidence of bladder cancer in patients treated with TKIs was higher than that in the general Japanese population. So far 19 patients have died and the median age at death was 79 (59 – 94) years. In these patients, 8 deaths were related to cancer and the others were caused by diseases associated with old age that were unrelated to the worsening of CML.

The introduction of TKIs has undoubtedly improved the prognosis of patients with CML. Based on the results of this investigation, the apparent increase in malignant diseases observed during the long-term follow-up of patients treated with TKIs was generally considered to be attributable to the aging of patients. We should however further investigate whether the higher incidence of bladder cancer seen in patients treated with TKIs is incidental or not.

No relevant conflicts of interest to declare.