Iwatsubo et al1 establish a strong link between workplace exposure from vitamin A synthesis and renal cell carcinoma (RCC). Their paper highlights how evaluation of screening data can identify cancer clusters, and reminds us that thorough investigations of selected cancer clusters can promote scientific discovery and cancer prevention.

In 1981, a French chemical plant began manufacturing vitamin A using a proprietary synthesis procedure (Navis procedure). Technical difficulties led to significant worker exposures to an intermediate chemical—chloracetyl C5. Unrelated to the Navis procedure, in 1986, the plant established an abdominal ultrasound screening programme to detect liver tumours in workers previously exposed to vinyl chloride monomer. The screening programme was extended to cover chloracetyl C5 exposed workers in 1992.

Screening identified RCC in 10 male plant workers during 1994 through 2002.2 Nine of the men synthesised vitamin A. The reported standardised incidence ratio for RCC among plant employees during this time …