Evaluation of Cancer Incidence in Census Tracts 3114 and 3116 ...

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1. Massachusetts Department Of Public Health Bureau of Environmental Health, Community Assessment Program Evaluation of Cancer Incidence in Census Tracts 3114 and 3116 in…
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  • 1. Massachusetts Department Of Public Health Bureau of Environmental Health, Community Assessment Program Evaluation of Cancer Incidence in Census Tracts 3114 and 3116 in Lowell, Massachusetts 1982-2001 July 2007
  • 2. Evaluation of Cancer Incidence in Census Tracts 3114 and 3116 in Lowell, Massachusetts ...........................................................................................................................1 1982-2001..................................................................................................................................................1 A. March 2005............................................................................................................................................1 I. INTRODUCTION.......................................................................................................................................1 II. METHODS FOR ANALYZING CANCER INCIDENCE....................................................................1 A. Case Identification/Definition...............................................................................................................1 B. Calculation of Standardized Incidence Ratios (SIRs)............................................................................3 C. Interpretation of a Standardized Incidence Ratio (SIR)........................................................................5 D. Calculation of the 95% Confidence Interval.........................................................................................6 E. Determination of Geographic Distribution of Cancer Cases................................................................7 III. RESULTS OF CANCER INCIDENCE ANALYSIS...........................................................................8 A. Cancer Incidence in CT 3114, 1982-1991.............................................................................................9 B. Cancer Incidence in CT 3114, 1992-2001.............................................................................................9 C. Cancer Incidence in CT 3116, 1982-1991.............................................................................................9 D. Cancer Incidence in CT 3116, 1992-2001...........................................................................................10 IV. Geographic and Temporal Distribution of Cancer Incidence in Lowell CTs 3114 and 3116.........10 V. Discussion and CONCLUSIONS...........................................................................................................10 VI. REFERENCES.......................................................................................................................................14 References....................................................................................................................................................13 References....................................................................................................................................................16 References....................................................................................................................................................21 References....................................................................................................................................................26 References....................................................................................................................................................30 References....................................................................................................................................................34 References....................................................................................................................................................37 References....................................................................................................................................................39 References....................................................................................................................................................42 i
  • 3. List of Figures Figure 1: Town and Census Tract Boundaries in Lowell, MA Figure 2: Location of the former Lowell Landfill site, Lowell, MA List of Tables Table 1: Cancer Incidence in CT 3114, 1982-1991 Table 2: Cancer Incidence in CT 3114, 1992-2001 Table 3: Cancer Incidence in CT 3116, 1982-1991 Table 4: Cancer Incidence in CT 3116, 1992-2001 Appendices Appendix A: Cancer Incidence Coding Definitions Appendix B: Risk Factor Information for Selected Cancer Types ii
  • 4. iii
  • 5. I. INTRODUCTION At the request of concerned residents, the Lowell Department of Inspectional Services, and Senator Steven C. Panagiotakos, the Community Assessment Program (CAP) of the Massachusetts Department of Public Health (MDPH), Bureau of Environmental Health conducted an evaluation of cancer incidence for census tracts (CTs) 3114 and 3116 in Lowell (see Figure 1). This evaluation was initiated due to community concerns about a suspected increase in the incidence of cancer specifically in the area surrounding the former Lowell Landfill site, located in CT 3114 on Westford Street in the western part of the city, near the border of CT 3116 (see Figure 2). This investigation provides a review of the pattern of nine cancer types in CTs 3114 and 3116 in Lowell and compares the incidence of these cancers with the cancer experience of the state of Massachusetts as a whole. Cancer incidence data for Lowell were obtained from the Massachusetts Cancer Registry (MCR) for the years 1982-2001. Two smaller time periods were evaluated, 1982-1991 and 1992-2001, to assess possible trends over time. The nine cancer types selected for this evaluation were based on potential associations with contaminants of concern at the former Lowell Landfill site and/or resident concern over suspected elevations of some cancer types. In addition to calculating cancer incidence rates, a qualitative analysis of the geographic distribution of individuals diagnosed with each of the nine types of cancer was conducted by mapping their residence at time of diagnosis. This was done to determine whether the geographic pattern of cancer in this area of the city was unusual. II. METHODS FOR ANALYZING CANCER INCIDENCE A. Case Identification/Definition 1
  • 6. Cancer incidence data (i.e., reports of new cancer diagnoses) for Lowell CTs 3114 and 3116 for the years 1982-2001 were obtained from the MCR, a division of the MDPH Bureau of Health Information, Statistics, Research and Evaluation (BHISRE). The MCR is a population-based surveillance system that began collecting information in 1982 on Massachusetts residents diagnosed with cancer in the state. All newly diagnosed cancer cases among Massachusetts residents are required by law to be reported to the MCR within 6 months of the date of diagnosis (M.G.L. c.111 s.111B). Nine cancer types were evaluated in this investigation, including cancers of the bladder, brain, breast, kidney, liver, lung and bronchus, pancreas and stomach as well as leukemia. [Coding for cancer types in this report follows the International Classification of Diseases for Oncology (ICD-O) system. See Appendix A for the incidence coding definitions used in this report for these cancer types.] These cancer types were selected for evaluation based on potential associations with contaminants of concern at the former Lowell Landfill site and/or resident concern over suspected elevations of some cancer types. All diagnoses reported to the MCR as primary cancers among residents of CT 3114 or CT 3116 for the nine cancer types were included in the analysis. Individuals diagnosed with cancer were selected for inclusion based on the address reported to the hospital or reporting medical facility at the time of diagnosis. The term "cancer" is used to describe a variety of diseases associated with abnormal cell and tissue growth. Epidemiologic studies have revealed that different types of cancer are individual diseases with separate causes, risk factors, characteristics and patterns of survival (Berg 1996). Cancers are classified by the location in the body where the disease originated (the primary site) and the tissue or cell type of the cancer (histology). Therefore, each of the cancer types reviewed in this report was evaluated separately. Cancers that occur as the result of the metastasis or the spread of a primary site cancer to another location in the body are not considered as separate cancers and therefore were not included in this analysis. 2
  • 7. It should be noted that duplicate records have been eliminated from the MCR data used in this report. Duplicate cases are additional reports of the same primary site cancer diagnosed in an individual by another health-care provider. The decision that a case was a duplicate and should be excluded from the analyses was made by the MCR after consulting with the reporting hospital/diagnostic facility and obtaining additional information regarding the histology and/or pathology of the case. However, reports of individuals with multiple primary site cancers were included as separate cases in this report. In general, a diagnosis of a multiple primary cancer is defined by the MCR as a new cancer in a different location in the body or a new cancer of the same histology (cell type) as an earlier cancer, if diagnosed in the same primary site (original location in the body) more than 2 months after the initial diagnosis (MCR 2003). B. Calculation of Standardized Incidence Ratios (SIRs) To determine whether an elevation occurred among individuals diagnosed with cancer in CTs 3114 and 3116, cancer incidence data were tabulated by gender according to eighteen age groups to compare the observed number of cancer diagnoses to the number that would be expected based on the statewide cancer rate. Standardized incidence ratios (SIRs) were then calculated for two time periods, 1982-1991 and 1992-2001, for each of the nine primary cancer types for each CT, in order to evaluate patterns or trends in cancer incidence over time. To calculate SIRs, it is necessary to obtain accurate population information. The population figures used in this analysis were interpolated based on 1980, 1990, and 2000 U.S. census data for the two CTs in Lowell (U.S. DOC 1980, 1990, and 2000). Midpoint population estimates were calculated for each time period evaluated (i.e., 1986 and 1996). To estimate the population between census years, an assumption was made that the change in population occurred at a constant rate throughout the ten-year interval between each census.1 A CT is a geographic subdivision of a city or town designated by the United States 1 Using slightly different population estimates or statistical methodologies, such as grouping ages differently or rounding off numbers at different points during calculations, may produce results slightly different from those published in this report. 3
  • 8. Census Bureau. Because age group and gender-specific population information is necessary to calculate incidence rates, the CT is the smallest geographic area for which cancer rates can be accurately calculated. Specifically, a CT is a smaller statistical subdivision of a county as defined by the U.S. Census Bureau. CTs usually contain between 2,500 and 8,000 persons and are designed to be homogenous with respect to population characteristics (U.S. DOC 1990). Twenty-seven CTs are within the city of Lowell. 4
  • 9. SIRs were not calculated for some cancer types in the smaller time periods and/or CTs due to the small number of observed cases (less than five). It is standard BHISRE policy not to calculate rates with fewer than five observed diagnoses. However, the expected number of diagnoses was calculated during each time period and for each CT, and the observed and expected numbers of diagnoses were compared to determine whether excess numbers of cancer diagnoses were occurring. C. Interpretation of a Standardized Incidence Ratio (SIR) An SIR is an estimate of the occurrence of cancer in a population relative to what might be expected if the population had the same cancer experience as a larger comparison population designated as "normal" or average. Usually, the state as a whole is selected to be the comparison population. Using the state of Massachusetts as a comparison population provides a stable population base for the calculation of incidence rates. Specifically, an SIR is the ratio of the observed number of cancer diagnoses in an area to the expected number of diagnoses multiplied by 100. The population structure of each town is adjusted to the statewide incidence rate to calculate the number of expected cancer diagnoses. The SIR is a comparison of the number of cases in the specific area (i.e., city/town or census tract) to the statewide rate. Comparison of SIRs between towns or census tracts is not possible because each community has different population characteristics. An SIR of 100 indicates that the number of cancer diagnoses observed in the population being evaluated is equal to the number of cancer diagnoses expected in the comparison or "normal" population. An SIR greater than 100 indicates that more cancer diagnoses occurred than were expected, and an SIR less than 100 indicates that fewer cancer diagnoses occurred than were expected. Accordingly, an SIR of 150 is interpreted as 50% more cancer diagnoses than the expected number; an SIR of 90 indicates 10% fewer cancer diagnoses than expected. 5
  • 10. Caution should be exercised, however, when interpreting an SIR. The interpretation of an SIR depends on both the size and the stability of the SIR. Two SIRs can have the same size but not the same stability. For example, an SIR of 150 based on four expected cases and six observed diagnoses indicates a 50% excess in cancer, but the excess is actually only two diagnoses. Conversely, an SIR of 150 based on 400 expected diagnoses and 600 observed diagnoses represents the same 50% excess in cancer, but because the SIR is based upon a greater number of diagnoses, the estimate is more stable. It is very unlikely that 200 excess diagnoses of cancer would occur by chance alone. As a result of the instability of incidence rates based on small numbers of diagnoses, SIRs were not calculated when fewer than five diagnoses were observed for a particular cancer type. D. Calculation of the 95% Confidence Interval To help interpret or measure the stability of an SIR, the statistical significance of each SIR was assessed by calculating a 95% confidence interval (95% CI) to determine if the observed number of diagnoses is “significantly different” from the expected number or if the difference may be due solely to chance (Rothman and Boice 1982). Specifically, a 95% CI is the range of estimated SIR values that have a 95% probability of including the true SIR for the population. If the 95% CI range does not include the value 100, then the study population is significantly different from the comparison or "normal" population. "Significantly different" means there is less than a 5% chance that the observed difference (either increase or decrease) is the result of random fluctuation in the number of observed cancer diagnoses. 6
  • 11. For example, if a confidence interval does not include 100 and the interval is above 100 (e.g., 105–130), there is a statistically significant excess in the number of cancer diagnoses. Similarly, if the confidence interval does not include 100 and the interval is below 100 (e.g., 45–96), the number of cancer diagnoses is statistically significantly lower than expected. If the confidence interval range includes 100, the true SIR may be 100. In this case, it cannot be determined with certainty that the difference between the observed and expected number of diagnoses reflects a real cancer increase or decrease or is the result of chance. It is important to note that statistical significance does not necessarily imply public health significance. Determination of statistical significance is just one tool used to interpret SIRs. In addition to the range of the estimates contained in the confidence interval, the width of the confidence interval also reflects the stability of the SIR estimate. For example, a narrow confidence interval, such as 103–115, allows a fair level of certainty that the calculated SIR is close to the true SIR for the population. A wide interval, for instance 85–450, leaves considerable doubt about the true SIR, which could be much lower than or much higher than the calculated SIR. This would indicate an unstable statistic. Again, due to the instability of incidence rates based on small numbers of diagnoses, statistical significance was not assessed when fewer than five diagnoses were observed. E. Determination of Geographic Distribution of Cancer Cases 7
  • 12. In addition to calculating SIRs, the address at the time of diagnosis for each individual diagnosed with one of the nine cancer types in CTs 3114 and 3116 was mapped using a computerized geographic information system (GIS) (ESRI 2005). This allowed assignment of CT location for each individual diagnosed with cancer as well as an evaluation of the spatial distribution of the individuals at a smaller geographic level within CTs (i.e., neighborhoods). The geographic pattern was determined using a qualitative evaluation of the point pattern of cancer diagnoses in CTs 3114 and 3116. This evaluation included consideration of the population density variability of each CT through the use of GIS-generated population density overlays. In instances where the address information from the MCR was incomplete, that is, did not include specific streets or street numbers, efforts were made to research those individuals diagnosed with cancer (e.g., by using telephone books issued within 2 years of an individual's diagnosis or searching files via the Registry of Motor Vehicles). For confidentiality reasons, it is not possible to include maps showing the locations of individuals diagnosed with cancer in this report. [Note: MDPH is bound by state and federal patient privacy and research laws not to reveal the name or any other identifying information of an individual diagnosed with cancer and reported to the MCR.] III. RESULTS OF CANCER INCIDENCE ANALYSIS The following sections present cancer incidence rates for the two CTs in Lowell during the 20-year time period 1982-2001. As shown in Figure 2, the former Lowell Landfill was located in CT 3114, near the border with CT 3116. To evaluate possible trends over time, these data were analyzed by two smaller time periods, 1982-1991 and 1992-2002. Tables 1 and 2 summarize cancer incidence data for CT 3114 for the two time periods, 1982-1991 and 1992-2001, while Tables 3 and 4 summarize cancer incidence data for CT 3116 for each time period. SIRs were not calculated for some cancer types, in these smaller time periods and/or CTs, due to the small number of observed cases (less than five). As previously mentioned, the expected number of diagnoses was calculated during each time period and for each CT, and the observed and expected numbers of diagnoses were compared to determine whether excess numbers of cancer diagnoses were occurring. 8
  • 13. Risk factor summaries for each type of cancer evaluated are included in Appendix B. A. Cancer Incidence in CT 3114, 1982-1991 In general, with some exceptions noted below, the incidence rates of the nine cancer types evaluated in Lowell CT 3114 were approximately at or near the rates expected during 1982-1991 (see Table 1). A slight elevation among females diagnosed with breast cancer was noted, 29 females were diagnosed while 26 would be expected
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