Trends of incidence and survival of patients with chronic myelomonocytic leukemia between 1999 and 2014: A comparison between Swiss and American population-based cancer registries

Background: Chronic myelomonocytic leukemia (CMML) is a rare hematopoietic malignancy. Treatment with hypomethylating agents (HMA) was introduced between 2004 and 2006 but its impact on population-based survival remains controversial. The aim of this study was to investigate epidemiological characteristics and survival before and after introduction of HMA treatment.

Methods: We performed a population-based analysis of CMML cases reported to the Cantonal Cancer Registries in Switzerland (SWISS) and the Surveillance, Epidemiology, and End Results (SEER) Program from the United States for 1999-2006 (before HMA) and 2007-2014 (after HMA). Time trends were compared for these two time periods.

Results: 423 and 4144 new CMML cases were reported to the SWISS and SEER registries, respectively. We observed an increasing proportion of older patients ≥75 years in the SWISS (50.3%-62.3%) compared to a decreasing one in the SEER population (59.1%-55.1%). Age standardized incidence-rates were similar and remained stable in both countries (0.32-0.38 per 100'000 py). Relative survival (RS) improved significantly in the SEER (3 years 27%-37%; 5 years 19%-23%; p < 0.001 for both) but remained stable in the SWISS population (3 years 48% to 40%; 5 years 34% to 26%; n.s. for both).

Conclusions: With the exception of opposing age-trends, epidemiologic characteristics are similar in both countries and comparable to other population-based registries. RS remains poor and different time trends of population-based survival cannot be faithfully explained by HMA but most likely by changes in diagnostic accuracy within prognostically distinct age-groups.