Increased stomach cancer risk following radiotherapy for testicular cancer.

BACKGROUND: Abdominal radiotherapy for testicular cancer (TC) increases risk for second stomach cancer, although data on the radiation dose-response relationship are sparse. METHODS: In a cohort of 22,269 5-year TC survivors diagnosed during 1959-1987, doses to stomach subsites were estimated for 92 patients who developed stomach cancer and 180 matched controls. Chemotherapy details were recorded. Odds ratios (ORs) were estimated using logistic regression. RESULTS: Cumulative incidence of second primary stomach cancer was 1.45% at 30 years after TC diagnosis. The TC survivors who received radiotherapy (87 (95%) cases, 151 (84%) controls) had a 5.9-fold (95% confidence interval (CI) 1.7-20.7) increased risk of stomach cancer. Risk increased with increasing stomach dose (P-trend<0.001), with an OR of 20.5 (3.7-114.3) for ⩾50.0 Gy compared with <10 Gy. Radiation-related risks remained elevated ⩾20 years after exposure (P<0.001). Risk after any chemotherapy was not elevated (OR=1.1; 95% CI 0.5-2.5; 14 cases and 23 controls). CONCLUSIONS: Radiotherapy for TC involving parts of the stomach increased gastric cancer risk for several decades, with the highest risks after stomach doses of ⩾30 Gy. Clinicians should be aware of these excesses when previously irradiated TC survivors present with gastrointestinal symptoms and when any radiotherapy is considered in newly diagnosed TC patients.

Pancreatic cancer risk after treatment of Hodgkin lymphoma.

BACKGROUND: Although elevated risks of pancreatic cancer have been observed in long-term survivors of Hodgkin lymphoma (HL), no prior study has assessed the risk of second pancreatic cancer in relation to radiation dose and specific chemotherapeutic agents. PATIENTS AND METHODS: We conducted an international case-control study within a cohort of 19 882 HL survivors diagnosed from 1953 to 2003 including 36 cases and 70 matched controls. RESULTS: Median ages at HL and pancreatic cancer diagnoses were 47 and 60.5 years, respectively; median time to pancreatic cancer was 19 years. Pancreatic cancer risk increased with increasing radiation dose to the pancreatic tumor location (Ptrend = 0.005) and increasing number of alkylating agent (AA)-containing cycles of chemotherapy (Ptrend = 0.008). The odds ratio (OR) for patients treated with both subdiaphragmatic radiation (≥10 Gy) and ≥6 AA-containing chemotherapy cycles (13 cases, 6 controls) compared with patients with neither treatment was 17.9 (95% confidence interval 3.5-158). The joint effect of these two treatments was significantly greater than additive (P = 0.041) and nonsignificantly greater than multiplicative (P = 0.29). Especially high risks were observed among patients receiving ≥8400 mg/m(2) of procarbazine with nitrogen mustard or ≥3900 mg/m(2) of cyclophosphamide. CONCLUSION: Our study demonstrates for the first time that both radiotherapy and chemotherapy substantially increase pancreatic cancer risks among HL survivors treated in the past. These findings extend the range of nonhematologic cancers associated with chemotherapy and add to the evidence that the combination of radiotherapy and chemotherapy can lead to especially large risks.

Risk of treatment-related esophageal cancer among breast cancer survivors.

BACKGROUND: Radiotherapy for breast cancer may expose the esophagus to ionizing radiation, but no study has evaluated esophageal cancer risk after breast cancer associated with radiation dose or systemic therapy use. DESIGN: Nested case-control study of esophageal cancer among 289 748 ≥5-year survivors of female breast cancer from five population-based cancer registries (252 cases, 488 individually matched controls), with individualized radiation dosimetry and information abstracted from medical records. RESULTS: The largest contributors to esophageal radiation exposure were supraclavicular and internal mammary chain treatments. Esophageal cancer risk increased with increasing radiation dose to the esophageal tumor location (P(trend )< 0.001), with doses of ≥35 Gy associated with an odds ratio (OR) of 8.3 [95% confidence interval (CI) 2.7-28]. Patients with hormonal therapy ≤5 years preceding esophageal cancer diagnosis had lower risk (OR = 0.4, 95% CI 0.2-0.8). Based on few cases, alkylating agent chemotherapy did not appear to affect risk. Our data were consistent with a multiplicative effect of radiation and other esophageal cancer risk factors (e.g. smoking). CONCLUSIONS: Esophageal cancer is a radiation dose-related complication of radiotherapy for breast cancer, but absolute risk is low. At higher esophageal doses, the risk warrants consideration in radiotherapy risk assessment and long-term follow-up.

Bladder and kidney cancer following cyclophosphamide therapy for non-Hodgkin's lymphoma.

BACKGROUND: Cyclophosphamide is an established bladder carcinogen, but few studies have examined the relationship between dose and effect. The largest analysis to date included only seven cases of bladder cancer. No investigation has estimated the risk of kidney cancer. PURPOSE: The purpose of this study was to quantify the risk of bladder and kidney cancer following cyclophosphamide therapy. METHODS: Within a cohort of 6171 two-year survivors of non-Hodgkin's lymphoma (NHL), 48 patients with secondary cancer of the urinary tract were identified and matched to 136 control subjects with NHL who did not develop a second malignancy. Detailed information on chemotherapeutic drugs and cumulative dose received was collected for all subjects. Radiation dose to the target organ was estimated from individual radiotherapy records. Evaluations of the risk of second cancer as a result of treatment with cyclophosphamide alone, radiation alone, or both therapies were made relative to those patients who were exposed to neither treatment modality. RESULTS: A significant 4.5-fold risk of bladder cancer (95% confidence interval [CI] = 1.5-13.6) followed therapy with cyclophosphamide, and risk was dependent upon cumulative dose. Among patients who received a total amount of cyclophosphamide of less than 20 g, a nonsignificant 2.4-fold risk of bladder cancer was apparent. Significantly elevated sixfold (95% CI = 1.3-29) and 14.5-fold (95% CI = 2.3-94) risks of bladder malignancy followed cumulative doses of 20-49 g and 50 g or more, respectively (P value for trend = .004). Radiotherapy given without cyclophosphamide was associated with a nonsignificant increased risk of bladder malignancy. Excess bladder cancer risk following treatment with both radiotherapy and cyclophosphamide was as expected if individual risks were summed. Neither radiotherapy nor cyclophosphamide was associated with excesses of kidney cancer. CONCLUSIONS: Cyclophosphamide-related bladder cancer is dose dependent. For patients given cumulative doses between 20 and 49 g, the absolute risk of bladder cancer is on the order of three excess cancers per 100 NHL patients after 15 years of follow-up. At cumulative doses of 50 g or more, the excess risk increases to approximately seven excess bladder cancers per 100 NHL patients. IMPLICATIONS: The strong dose-response relationship and high absolute risk of bladder cancer underscore the importance of limiting the cumulative dose of cyclophosphamide to what is required to achieve therapeutic end points. The risk of secondary bladder malignancy and other late sequelae of therapy must be carefully weighted against the curative gains provided by cyclophosphamide. Moreover, long-term side effects of therapy that might be acceptable in cancer treatment may need to be re-evaluated for patients with non-neoplastic disorders.

Risk of leukemia following treatment for non-Hodgkin's lymphoma.

BACKGROUND: There have been few evaluations of the risk of acute nonlymphocytic leukemia (ANLL) following therapy for non-Hodgkin's lymphoma (NHL). Further, the relationship between cumulative dose of cytotoxic drug, radiation dose to active bone marrow, and the risk of ANLL following NHL have not been well described. PURPOSE: Our purpose was to examine the risk of ANLL in relationship to all prior treatment for NHL. METHODS: Within a cohort study of 11,386 2-year survivors of NHL, 35 case patients with secondary ANLL were identified and matched to 140 controls with NHL who did not develop ANLL. The primary eligibility criteria for the cohort included a diagnosis of NHL as a first primary cancer from January 1, 1965, through December 31, 1989; age 18 through 70 years at the time of initial diagnosis; and survival for 2 or more years without the development of a second invasive primary malignancy. Detailed information on chemotherapeutic drugs and radiotherapy was collected for all patients. Standard conditional logistic regression programs were used to estimate the relative risk (RR) of ANLL associated with specific therapies by comparing the exposure histories of case patients with individually matched controls. RESULTS: Significant excesses of ANLL followed therapy with either prednimustine (RR = 13.4; 95% confidence interval [CI] = 1.1-156; P trend for dose < .05) or regimens containing mechlorethamine and procarbazine (RR = 12.6; 95% CI = 2.0-79; P < .05). Elevated risks of leukemia following therapy with chlorambucil were restricted to patients given cumulative doses of 1300 mg or more (RR = 6.5; 95% CI = 1.6-26; P < .05). Cyclophosphamide regimens were associated with a small, nonsignificant increased risk of ANLL (RR = 1.8;95% CI = 0.7-4.9), with most patients receiving relatively low cumulative doses (< 20,000 mg). Radiotherapy given at higher doses without alkylating agents was linked to a nonsignificant threefold risk of ANLL compared with lower dose radiation or no radiotherapy. CONCLUSIONS: Our results suggest that prednimustine may be a human carcinogen, with a positive dose-response gradient evident for ANLL risk. The low, nonsignificant risk of leukemia associated with cyclophosphamide was reassuring because this drug is commonly used today. Despite the excesses of ANLL associated with specific therapies, secondary leukemia remains a rare occurrence following NHL. Of 10,000 NHL patients treated for 6 months with selected regimens including low cumulative doses of cyclophosphamide and followed for 10 years, an excess of four leukemias might be expected.

Does a centralized radiotherapy system provide adequate access to care?

PURPOSE: In the Canadian province of Ontario, all radiotherapy is provided by a centrally managed provincial network of nine cancer centers. The primary goal of this study was to determine whether this highly centralized radiotherapy system provides adequate and equitable access to care for the province's dispersed population. METHODS: The Ontario Cancer Registry (OCR) was used to identify 295,386 cases of invasive cancer, excluding nonmelanoma skin cancer, which were diagnosed in Ontario between 1984 and 1991. Electronic radiotherapy records from each of the province's radiotherapy centers were linked to the registry at the level of the individual case. RESULTS: The proportion of incident cases treated with radiotherapy was 18.8% at 4 months after diagnosis, 23.7% at 1 year, 25.8% at 2 years, 28.2% at 5 years, and 29.1% at 8 years. These rates of radiotherapy use are much lower than the accepted national and international targets, and lower than rates reported from other jurisdictions. The rate of radiotherapy use at 1 year varied significantly from county to county across Ontario (range, 18.6% to 32.4%; P < 10(-6)), and the highest rates were recorded in communities close to radiotherapy centers. There was a common geographic pattern of rate variations among several disease groups, including breast cancer, lung cancer, the genitourinary malignancies, and the gastrointestinal malignancies. CONCLUSION: The low and uneven rates of radiotherapy use across the province indicate that Ontario's centralized radiotherapy system does not, at present, provide adequate or equitable access to care.

Second cancers among long-term survivors of Hodgkin's disease diagnosed in childhood and adolescence.

PURPOSE: To quantify the risk of second cancers among long-term survivors of Hodgkin's disease (HD) diagnosed before 21 years of age and to explore sex-, age-, and site-related differences. PATIENTS AND METHODS: We analyzed data from 5,925 pediatric HD patients, including 2,646 10-year and 755 20-year survivors, who were reported to 16 population-based cancer registries in North America and Europe between 1935 and 1994. RESULTS: A total of 157 solid tumors (observed/expected ratio [O/E] = 7.0; 95% confidence interval [CI], 5.9 to 8.2.) and 26 acute leukemias (O/E = 27.4; 95% CI, 17.9 to 40. 2) were reported. Risk of solid tumors remained significantly increased among 20-year survivors (O/E = 6.6, observed [O] = 40, cumulative risk = 6.5%) and persisted for 25 years (O/E = 4.6, O = 15, cumulative risk = 11.7%). Temporal trends for cancers of thyroid, female breast, bone/connective tissue, stomach, and esophagus were consistent with the late effects of radiotherapy. Greater than 50-fold increased risks were observed for tumors of the thyroid and respiratory tract (one lung and one pleura) among children treated before age 10. At older ages (10 to 16 years), the largest number of second cancers occurred in the digestive tract (O/E = 19.3) and breast (O/E = 22.9). Risk of solid tumors increased with decreasing age at HD on a relative but not absolute scale. CONCLUSION: Children and adolescents treated for HD experience significantly increased risks of second cancers at various sites for 2 to 3 decades. Although our results reflect the late effects of past therapeutic modalities, they underscore the importance of lifelong follow-up of pediatric HD patients given early, more aggressive treatments.

p53 mutations in cyclophosphamide-associated bladder cancer.

Cyclophosphamide is a known bladder carcinogen, with cumulative dose directly related to increased risk. There is no consensus, however, on which major cyclophosphamide metabolite (i.e., acrolein or phosphoramide mustard) drives bladder carcinogenesis. We examined 19 cyclophosphamide-related bladder tumors to test the hypothesis that they might contain somatic mutations in the p53 tumor suppressor gene that could link a specific metabolite to the etiology of these cancers. Forty-three % (9 of 19) of the cases had a mutation in p53, with a predominance at G:C bp (7 of 9, 77%), a preference for non-CpG sites (6 of 7, 86%), and frequent G:C-->A:T transitions (5 of 7, 71%). The p53 mutation spectrum of these cyclophosphamide-associated bladder cancers differed significantly from patterns reported for sporadic (P = 0.020), smoking-related (0.043), and schistosomiasis-linked (P = 0.002) tumors but not arylamine-associated neoplasms (P = 0.860). Differences between the cyclophosphamide and arylamine-associated spectra included an unusual degree of clustering of exon 6 mutations (43% versus 17%, respectively) and an absence of multiple mutations in the former. Notably lacking in our series were G:C-->T:A transversions, the principal mutation associated with acrolein. Instead, the mutation spectrum matches the phosphoramide mustard adduction sequences determined by a repetitive primer-extension assay (P = 0.024), indicating that this metabolite might be a key mutagen in cyclophosphamide-related bladder cancer.

Cancer incidence registration and trends in Ontario.

The Ontario Cancer Registry (OCR) contains information on the incidence, mortality and survival of cancer in Ontario. The OCR refers to the population of Ontario, which is currently more than 9 million people. Cancer registration is accomplished by the computerised linkage of records collected routinely for other purposes. Incidence data are available from the OCR beginning in 1964. Incidence rates, age-standardised to the World Standard Population, are presented for Ontario in two recent 5-year periods (1979-1983 and 1984-1988). Age-specific rates are also presented for selected sites. The most common cancer sites, in terms of Ontario incidence rates, were similar to those reported from other registries. In males, these were cancers of the lung, prostate, colon, bladder and rectum. In females, these were cancers of the breast, lung, colon, body of the uterus and ovary. The potential effects of changes in medical services, screening practices and risk factor prevalence on the incidence rates and trends are discussed.

A population-based study of the effectiveness of breast conservation for newly diagnosed breast cancer.

PURPOSE: Our objective was to evaluate the effectiveness of breast conservation for newly diagnosed breast cancer. Effectiveness was operationalized as two outcomes within 5 years of the diagnosis of breast cancer: the probability of mastectomy-free survival (either death or mastectomy count as event, whichever comes first), and the probability of mastectomy conditional on survival (mastectomy counts as event, observations censored at death). METHODS AND MATERIALS: We linked records of 46,687 new cases of breast cancer from 1982 to 1991 in the Ontario Cancer Registry to records of surgery from 1982 to 1995, radiotherapy (RT) from 1982 to 1992, and median household income from the 1986 census. We labeled breast surgery within 4 months and postoperative RT within 12 months of diagnosis as treatment for newly diagnosed breast cancer. Surgery was categorized as mastectomy, lumpectomy plus RT, lumpectomy alone, or no surgical procedure. Among cases that did not undergo mastectomy within 4 months of diagnosis, we labeled mastectomy subsequent to 4 months after diagnosis as treatment failure. We performed life-table analysis and Cox proportional hazards regression, to describe the probability of mastectomy conditional on survival and the probability of mastectomy-free survival. RESULTS: A total of 16,279 cases underwent lumpectomy as the maximum procedure on the breast within 4 months of diagnosis, and 49.7% of these received postoperative RT. Compared to the provincial mean, regions with higher rates of lumpectomy plus RT have higher probability of mastectomy-free survival and lower probability of mastectomy conditional upon survival 5 years after diagnosis of breast cancer. CONCLUSIONS: These findings are consistent with a hypothesis that breast conservation is effective in the overall breast cancer population of Ontario within the first 5 years after diagnosis.

Cancer mortality among Chinese migrants: a review.

BACKGROUND: Epidemiological studies of cancer among migrant groups are beneficial in that they can provide insight into genetic and environmental factors in disease aetiology. Seven studies in the epidemiological literature have examined cancer mortality in migrants from China; methodological features and findings, which display remarkable consistencies between studies, are reviewed here. METHODS: Papers were included that compare site-specific cancer mortality patterns in first and second generation migrants to the experience in the host regions using vital statistics and census data. Rates had to be standardized either indirectly (using age-specific rates from the host regions) or directly (using a standard age structure) and standardized mortality ratios (SMR) or rate ratios (RR) were calculated. RESULTS: Migrant males had overall mortality from cancer that was often in significant excess compared to the host experience; results for females (for overall cancer) were equivocal. Both sexes had large and significant excess mortality from nasopharyngeal and liver cancer; SMR and RR were also consistently elevated for cancers of the stomach and oesophagus. There was notable attenuation in the high risk at these four sites in the second generation. All studies reported pronounced and significant reduced risk for prostatic cancer and female breast cancer, with little or no increase in mortality in the second generation. The SMR and RR also tended to be below unity for brain, bladder and kidney cancer. CONCLUSIONS: The results of this review indicate that cancer risk at several sites among Chinese migrants appears to be in transition, and that these findings are consistent across studies.

Prostate-specific antigen utilization in Ontario: extent of testing in patients with and without cancer.

OBJECTIVES: To ascertain the extent of prostate-specific antigen (PSA) testing in patients with prostate cancer (PC), with other cancers (OC), and with no cancer (NC) in two clinical laboratory databases. DESIGN AND METHODS: PSA test records were obtained from a tertiary care hospital, Sunnybrook Health Science Centre (SHSC) and from a private laboratory, Gamma-Dynacare Medical Laboratories (GDL), during the period 1988 to 1995. These records were linked with the Ontario Cancer Registry (OCR) to establish a diagnosis of PC, OC, or NC. Trends in PSA testing according to diagnostic category, testing laboratory, patient age (by decade), and PSA value (in microgram/L) were determined. RESULTS: Major cancer sites identified in the patients tested for PSA were prostate (60%), bladder and colon (7% each), lung (5%), kidney (3%), and rectum (3%). There were 11,867 patients (8.5%) with PC, 8,002 (5.9%) with OC, and 118,954 (86%) with NC. The total number of PSA tests performed on these patients was 230,756, of which 21% were on PC, 5% on OC, and 74% on NC; of these tests, 64% were performed through GDL and 36% through SHSC. The mean (median) number of tests per patient was: PC, 4.0 (2); OC, 1.4 (1); and NC, 1.5 (1). For PC 89% and for OC 72% of all tests occurred after diagnosis. Between 1990 and 1995 the number of PSA tests increased two-fold in PC and OC, and 20-fold in NC. We estimate that about one-half of the PSA tests in the NC group were for screening purposes. The proportion of PSA tests occurring in PC, OC, and NC for patients 50 to 70 years of age was 41%, 50%, and 63%, respectively; for patients over 70 years of age, this proportion was 58%, 46%, and 22% respectively; and for patients under 50 it was 1%, 4%, and 15%, respectively. Between 1990 and 1995, the largest increase in testing frequency was in the NC group, particularly in patients 50 to 70 years of age, which was accompanied by a decrease in patients over 70. Less than 10% of testing occurred in patients under 50 in all diagnostic groups. We estimate that about 26% of PSA screening tests in NC occurred outside the guidelines for patient age. Between 1988 and 1995, the proportion of PSA results below our detection limit (< 0.2 micrograms/L) showed a steady rise in the PC group, as did the proportion between 0.2 and 3.9 micrograms/L; these were accompanied by a fall in the proportion > 20.0 micrograms/L. However, the proportion of PSA results within these ranges did not change much during the same time period for the OC and NC groups. At cutoffs of PSA = 4.0 micrograms/L (or PSA = 10.0 micrograms/L), estimates of clinical specificity were 84.0% (or 96.3%), and of clinical sensitivity were 83.4% (or 47.1%). CONCLUSIONS: Most (86%) PSA testing occurred in men with NC, consistent with diagnosis or screening. There were more PSA tests per patient in PC than in OC, and most testing occurred after diagnosis. PSA testing in the NC group continues to increase rapidly. The proportion of PSA tests in patients over age 70 decreased in the order of PC > NC > OC. Between 1990 and 1995, there was an increase in the proportion of patients tested who were between 50 and 70 in the NC group, which may suggest more screening in this group. Over this same time period, there was an increase in the proportion of undetectable PSA values, possibly suggesting increased use of radical therapy; there was also a decrease in the proportion of PSA > 20 micrograms/L, possibly suggesting a decrease in the prevalence of advanced stage PC.

Lung cancer in women in the Niagara Region, Ontario: a case-control study.

A case-control study of the etiology of lung cancer in women was conducted in the Niagara Region of Ontario, because of local concerns about a high incidence of lung cancer. 51 female patients with lung cancer and 45 matched controls were interviewed. Information was collected about active and passive smoking, occupation and residential history. There was a strong association between active cigarette smoking and lung cancer (ever/never odds ratio 10.0; p less than .001) and 85% of the cases of lung cancer were attributed to active cigarette smoking. No other factors were significantly associated with lung cancer; there was weak evidence of an association between urban environment during childhood and lung cancer (p = 0.07). Associations between lung cancer and air pollution, and residential history, were not demonstrated, contrary to public perception. Thus, a previously reported excess of lung cancer in Niagara females is most likely attributable to cigarette smoking.

Use of surnames to identify individuals of Chinese ancestry.

The objectives of this study were to develop and test surname lists for identifying Chinese ancestry. The Ontario all-cause mortality database for the period 1982-1989 was randomly split into source and test data sets. Frequencies by birthplace were compiled for each surname in the source data set, by sex, and the surnames were weighted based on their positive likelihood ratios. Lists of Chinese surnames were then assembled based on varying cutoff levels, and screening performance indicators for each list were calculated, including sensitivity, specificity, positive and negative predictive values, post-test odds, positive likelihood ratio, and yield. The internally generated lists were evaluated in the test data set. Results indicated that surnames have a good potential to identify individuals of Chinese origin. In the source data set, at a cutoff level of 100 for males (217 surnames) and females (210 surnames), both sensitivity and the positive predictive value of the surname lists for males and females were very high, above 80%, and the positive likelihood ratio was above 600. In the test data set and using the same surname lists, the sensitivity, positive predictive value, and positive likelihood ratio remained at a high level: 73%, 81%, and 603, respectively, for males; and 73%, 84%, and 772, respectively, for females. Various scenarios and their methodological implications are discussed.

Leukemia after irradiation for endometrial cancer in Ontario.

BACKGROUND: In human studies, the risk of leukemia after ionizing radiation has been found to be increased more often than for any other cancer. It is useful to study patients with cancer treated with radiation because exposure can be measured accurately, follow-up may be long, and often a comparable and sizable nonexposed group exists. Women with endometrial cancer represent an excellent population for study because they meet these Developed Leukemia After Endometrial. METHODS: A population-based matched case-control study, nested among all patients with endometrial cancer diagnosed in Ontario, was undertaken to describe the relationship between radiation therapy and leukemia risk. Among 13,843 subjects treated from 1964 to 1987 who survived at least 1 year, 47 confirmed cases of leukemia were identified. Four control subjects were matched to each patient based on age, calendar year of diagnosis, and length of survival free of a second neoplasm. Medical records were abstracted, and radiation dose administered to active bone marrow was determined by dosimetry. RESULTS: An elevated risk of all leukemias other than chronic lymphocytic leukemia was observed, but only within the first 10 years after endometrial cancer treatment (odds ratio 12.0; 90% confidence interval 2.8-52.1). There was insufficient statistical evidence that risk was influenced by dose or type of radiation therapy. Nor was there any evidence that risk was influenced by age at endometrial cancer diagnosis or by calendar period at diagnosis. CONCLUSIONS: There is an increased risk of leukemia associated with radiation therapy for patients with endometrial cancer, but only within the first 10 years after treatment.

Patterns of initial management of node-negative breast cancer in two Canadian provinces. British Columbia/Ontario Working Group.

OBJECTIVE: To describe the patterns of initial management of node-negative breast cancer in Ontario and British Columbia and to compare the characteristics of the patients and tumours and of the physicians and hospitals involved in management. DESIGN: Retrospective, population-based, cohort study. PARTICIPANTS: All 942 newly diagnosed cases of node-negative breast cancer in 1991 in British Columbia and a random sample of 938 newly diagnosed cases in Ontario in the same year. OUTCOME MEASURES: Number and proportion of patients with newly diagnosed node-negative breast cancer who received breast-conserving surgery (BCS) or mastectomy and who received radiation therapy after BCS. RESULTS: BCS was used in 413 cases (43.8%) in British Columbia and in 634 cases (67.6%) in Ontario (p < 0.001). After BCS, radiation therapy was received by 378 patients (91.5% of those who had undergone BCS) in British Columbia and 479 patients (75.6% of those who had undergone BCS) in Ontario (p < 0.001). In both provinces, lower patient age, smaller tumour size, a noncentral unifocal tumour, absence of extensive ductal carcinoma in situ and initial surgery by a surgeon with an academic affiliation were associated with greater use of BCS. Lower patient age and larger tumour size were associated with greater use of radiation therapy after BCS in both provinces. CONCLUSION: Patient, tumour and physician factors are associated with the choice of initial management of breast cancer in these two Canadian provinces. However, the differences in management between the two provinces are only partly explained by these factors. Other possible explanations, such as the presence of provincial guidelines, differences in the organization of the health care system or differences in patient preference, require further research.

Association between socioeconomic status and cancer incidence in Toronto, Ontario: possible confounding of cancer mortality by incidence and survival.

OBJECTIVE: To observe the association between socioeconomic status (SES) and cancer incidence in a cohort of Canadians. DESIGN: Cases of primary malignant cancer (83,666) that arose in metropolitan Toronto, Ont., from 1986 to 1993 were ascertained by the Ontario Cancer Registry and linked by residence at the time of diagnosis to a census-based measure of SES. Socioeconomic quintile areas were then compared by cancer incidence. RESULTS: Significant associations between SES and cancer incidence in the hypothesized direction--greater incidence in low-income areas--were observed for 15 of 23 cancer sites. CONCLUSIONS: These findings, together with the recently observed consistent pattern of significant associations between SES and cancer survival in the United States and the equally consistent pattern of nonsignificant associations in Canada, support the notion that differences in cancer incidence alone explain the observed cancer mortality differentials by SES in Canada. The cancer mortality differential by SES observed in the United States is probably a function of differences in both incidence and length of survival, whereas in Canada such mortality differentials are more likely to be merely a function of differences in incidence by SES. This pattern of associations primarily implicates differences in the 2 health care systems; specifically, the more egalitarian access to preventive, investigative and therapeutic services available in the single-payer Canadian system.