Selection of neighborhood controls: logistics and fieldwork.

This paper describes the logistics and fieldwork involved in assembling 123 neighborhood controls for a case-control study investigating the relationship between cholecystectomy and right-side colon cancer. All neighborhood controls were matched pairwise to cases on sex, age at diagnosis (+/- years), and race. Eighty-six percent of the neighborhood controls were also matched on street of residence and the remaining 14% on census tract. Study subjects were contacted by mail and then interviewed by telephone with regard to their gastrointestinal surgical history. The mean number of necessary households contacted to obtain each control was nine. When data were stratified by age, the mean number of necessary households contacted increased with increasing age of the cases. Only 3.3% (35/1065) of the residents from these households refused complete participation in the telephone interview. The distribution of fieldwork activities by hours worked is also reported. Similar findings were observed for males and females. Neighborhood controls are a commonly used comparison series. Data from this report may be used to modify the general impression that assembling neighborhood controls can be a difficult task. We urge other investigators to report fieldwork activities used in identifying their control series. These data will be valuable in planning and budgeting case-control studies.

A case-control study of cholecystectomy and right-side colon cancer: the influence of alternative data sources and differential interview participation proportions on odds ratio estimates.

One hundred fifty patients with right-side colon cancer (i.e., patients with adenocarcinoma of the cecum or ascending colon) were compared to 150 matched left-side colon cancer controls (i.e., patients with adenocarcinoma of the descending or sigmoid colon) and to 123 neighborhood controls, Pittsburgh, Pennsylvania, Standard Metropolitan Statistical Area, 1975-1978. The gastrointestinal surgical history was ascertained for all study subjects so that the presence or absence of a history of cholecystectomy could be noted. Cholecystectomy history was obtained through telephone interviews and whenever possible subsequently validated from operative and pathology reports at time of cholecystectomy. Cholecystectomy history for the colon cancer patients was also abstracted from hospital records at time of colon cancer diagnosis with an attempt to confirm the gallbladder's status through operative reports, cholecystograms, and physical examinations. Hospital records and interviews for the colon cancer patients appeared to provide accurate exposure history. Point estimates of the odds ratios and confidence intervals for intra- and inter-data source comparisons (i.e., hospital records, interviews, and hospital records and interviews combined) were comparable with similar measures of effect. Consistent odds ratio estimates appeared in both left-side colon cancer controls (1.9) and neighborhood controls (1.89). The authors suggest that changes in bile acid metabolism following cholecystectomy may be associated an increased risk of right-side colon cancer.

Cholecystectomy and right-sided colon cancer: an epidemiological study.

The relation between prior cholecystectomy and right-sided colon cancer was investigated in a case-control study of 150 patients with histologically confirmed adenocarcinoma of the caecum or ascending colon and of two comparison groups. One comparison group consisted of 150 patients, matched for age, sex, and race, who had histologically confirmed adenocarcinoma of the descending or sigmoid colon and the other of 123 neighbourhood controls. Compared with left-sided cancer controls, the right-sided colon cancer cases had a relative risk of 1.87 for colon cancer after cholecystectomy. The relative risk was 1.86 when they were compared with the neighbourhood controls. When compared with both control groups relative risk was 1.77, with 95% confidence limits of 0.95 and 3.3 (p = 0.07). The increased risk of right-sided colon cancer after cholecystectomy may be associated with changes in biliary metabolism occurring after removal of a gall bladder.

Relationship between cholecystectomy and ascending colon cancer.

A retrospective study involving 706 sample cases of large bowel cancer grouped by subsite (ascending colon, transverse colon, descending colon, sigmoid colon, ana rectum), sex, and age identified during the Third National Cancer Survey (Pittsburgh SMSA, 1969--1971) was recently completed. The basic strategy of this comparative study was to determine whether the frequency distribution patterns of both demorgraphic characteristics and environmental factors differed among persons with subsite-specific cancer of the large bowel. Based on the information provided in the hospital records there was a gradient of previous cholecystectomy history from ascending colon cancer (10.5%) to rectal cancer (2.1%) in those patient records whose only gastrointestinal surgery indicated was cholecystectomy. For patient records in which the only surgical operation was cholecystectomy, or cholecystectomy plus other gastrointestinal surgery, the gradient persisted as one moved from the right to the left subsites of the large bowel. No relationship with respect to other types of gastrointestinal surgery was observed. It is clear, however, that a bias associated with the review of hospital records can account for this relationship and, therefore, the finding may be spurious. On the other hand, there is increasing evidence of a relationship between bile acid metabolism and carcinoma of the colon. It might be considered that the right side of the colon would be most likely affected by the potential carcinogenic effect of certain bile acid metabolites.