A Cancer Registrar's Guide to Collecting Industry and Occupation

Cancer prevention program planners and researchers rely on cancer registrars to
record the best information possible on potential cancer risk factors,
including potentially hazardous jobs held by cancer patients during their
working life.

The usual (longest-held) occupation and industry of workers can reveal the
national cancer burden by industry and occupation. Such information can also be
used to help discover jobs that may have a high risk for cancer or other
diseases and for which prevention efforts can be concentrated (or targeted).

More info - Source: National Institute for Occupational Safety and Health (NIOSH)