In October 2009, 23 scientists from 6 countries met at the International Agency for Research on Cancer (IARC) in Lyons, France, to re-assess the carcinogenicity of a number of chemical compounds, including formaldehyde.

In 2004 IARC reclassified formaldehyde from being a probable human carcinogen to being a known human carcinogen based on epidemiologic studies showing that occupational exposure to formaldehyde causes nasopharyngeal cancer.  At the 2009 meeting the scientists evaluated recent epidemiologic and mechanistic studies regarding formaldehyde and leukemia.  They concluded that the epidemiological evidence on leukemia had become stronger and that recent mechanistic studies provided new evidence that formaldehyde can cause blood-cell abnormalities that are characteristic of leukemia development.  Hence, they concluded there is sufficient evidence for a causal association of formaldehyde with leukemia.