A geographical analysis of breast cancer clustering in southern Ontario: generating hypotheses on environmental influences.

This article presents the results of spatial analysis of breast cancer clustering in southern Ontario. Data from the Cancer Care Ontario were analyzed using the Scan Statistic at the level of county, with further analysis conducted within counties that were identified as primary clusters at the dissemination area level. The results identified five counties as primary clusters of women diagnosed with breast cancer between 1986 and 2002: Essex (relative risk [RR] =1.096-1.061; p<0.001), Lambton (RR=1.05-1.167), Chatham-Kent (RR=1.133-1.191), Niagara (RR=1.228-1.290) and Toronto (RR=1.152-1.146). The within county analysis revealed several DAs with significantly higher (RR>3, p<0.05) rates of breast cancer, and supports our hypothesis that breast cancer risk in southern Ontario may be associated with industrial and environmental (such as pesticides) pollutants. Further research is needed to verify the environmental links within the identified clusters.

Cancer survival in Ontario, 1986-2003: evidence of equitable advances across most diverse urban and rural places.

OBJECTIVES: This study examined whether place and socio-economic status had differential effects on the survival of women diagnosed with breast cancer in Ontario during the 1980s and the 1990s. METHODS: The Ontario Cancer Registry provided 29,934 primary malignant breast cancer cases. Successive historical cohorts (1986-1988 and 1995-1997) were, respectively, followed until 1994 and 2003. Diverse places were compared: the greater metropolitan Toronto area, other cities, ranging in size from 50,000 to a million people, smaller towns and villages, and rural and remote areas. Socio-economic data for each woman's residence at the time of diagnosis were taken from population censuses. RESULTS: Very small cities (6%) with populations between 50,000 and 100,000 were the only places where breast cancer survival had advanced less compared to the province as a whole. Income gradients began to appear, however, in larger cities. Urban residents in the lowest income areas were significantly disadvantaged compared to the highest income areas during the 1990s, but not during the 1980s. CONCLUSION: This historical analysis of breast cancer survival evidenced remarkably equitable advances across nearly all of Ontario's diverse places. The most likely explanation for such substantial equity seems to be Canada's universally accessible, single-payer, health care system.