Cancer in a Montreal suburb: the investigation of a nonepidemic

In response to an alarming newspaper report of 34 cases of cancer in Chomedey, a suburb of Montreal, an epidemiologic survey was undertaken to determine the incidence of cancer in selected Montreal census tracts during the period 1975-79. Cases of cancer, were ascertained from the Quebec Tumour Registry, then age-standardized incidence ratios (SIRs) were calculated, the expected incidence being based on provincial age-specific rates and 1976 populations. The SIRs were significantly lower for males living in the implicated area (P less than 0.01) and were within expected limits for female residents. Further analysis revealed neither an elevated frequency of any particular tumour type nor a clustering of cases in this area. Following additional ascertainment of cases through the examination of hospital records, the SIRs were recalculated. No significant differences were found between those of the implicated area and those of the most demographically comparable census tract. Finally, an independent inquiry failed to uncover any actual or potential sources of environmental carcinogens.