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Cancer Overview

Did You Know?

Approximately 9% of all cancer deaths are thought to be related to environmental or occupational exposures.
Pie chart of primary causes of estimated cancer deaths

Cancer is not one disease, but a group of diseases. Research has shown that there are more than 100 different types of cancer, each with different causative (or risk) factors. A risk factor is anything that increases a person's chance of developing cancer and may include hereditary conditions, medical conditions or treatments, lifestyle factors, or environmental exposures. Cancer may be caused by several factors acting together over time. The World Health Organization (WHO) estimates that 30% of cancer could be prevented, mainly by not using tobacco, having a healthy diet, being physically active and preventing infections that may cause cancer. In general, most cancers have a long period of development (also known as a latency period) that can range from 10 to 50 years. While not much is known about the latency period for cancers that occur in children, it is assumed to be considerably shorter than in adults.

Cancer is common. According to the American Cancer Society, one in two men and one in three women will develop cancer during his or her lifetime. For this reason, cancers often appear to occur in “clusters,” and it is understandable that someone may perceive that there are an unusually high number of cancer diagnoses in their neighborhood or town. Upon close examination, many of these “clusters” are not unusual increases, as first thought, but are related to such factors as local population density, individuals who possess related behaviors or risk factors for cancer, or chance fluctuations in occurrence. Sometimes higher rates that occur over time are due to improved diagnostic techniques and changes in data collection or recording methods. Others, however, are unusual; that is, they represent a true excess of cancer in a workplace, a community, or among a subgroup of people. A suspected cluster is more likely to be genuine if it involves a large number of diagnoses of one type of cancer, a rare type of cancer, or diagnoses occurring among individuals in age groups not usually affected by that cancer type. These types of clusters may warrant further public health investigation.

Cancer incidence data provided on this website are obtained from the Massachusetts Cancer Registry (MCR) within the MDPH Office of Data Management and Outcomes Assessment. The MCR is a population-based cancer registry that collects information on new diagnoses of cancer in Massachusetts.

The MA EPHT website presents cancer data using two different types of statistics: direct incidence rates and standardized incidence ratios. For more information on these statistics, select the Direct Incidence Rates and Standardized Incidence Ratios (SIRs) tabs located at the top of this page.

Data Considerations

When reviewing and interpreting cancer incidence data, it is important to consider the following:

  • Data will only be presented to the public if the confidentiality rules of MDPH and the Massachusetts Cancer Registry (MCR) are met. These are rules requiring data aggregation and suppression to protect privacy.
  • Statistical significance for SIRs is assessed to determine if the observed number of diagnoses is statistically significantly different from the expected number of cancer diagnoses (based on the statewide experience), or if the difference may be due solely to chance. Statistical significance is determined by the 95% confidence interval.
  • MA EPHT incorporates the use of the Relative Standard Error (RSE) when assessing statistical stability. The RSE which provides a measure of reliability for direct incidence rates and SIRs. When the RSE is greater than 30%, the rate is unstable and caution should be exercised when interpreting results.
  • Numbers and rates may differ slightly from those contained in other publications. These differences may be due to file updates, differences in calculation methods (such as grouping ages differently or rounding off numbers at different points in calculations), and updates or differences in population estimates.

For additional information, please read the FAQ.

Information about Cancer Data on this Website

Cancer data are presented on the MA EPHT website using two different types of statistics:

  • Direct Incidence Rates

    A direct incidence rate is the most appropriate statistic to compare cancer incidence in one relatively large area to another relatively large area (such as one county to another).

  • Standardized Incidence Ratios (SIRs)

    An SIR is the most appropriate statistic to examine cancer incidence in a small area, such as a community or a census tract within a community, and compare it to cancer incidence in a large, stable population (such as a state).

Direct Incidence Rates versus Standardized Incidence Ratios (SIRs)

It is important to emphasize the difference between the two types of cancer incidence rates that are presented on the MA EPHT portal. The direct age-adjusted cancer incidence rate is most appropriately used for larger, more stable study populations, such as a state or county. Because of the way it is calculated, it may be used to compare the cancer incidence rate of one geographic area to another (such as one county to another).

The other statistic, the standardized incidence ratio (SIR), is most appropriately used when the population is small, such as that of a community or a census tract. It is used to evaluate whether the occurrence of cancer within a community or a census tract differs from that of the state as a whole. The SIRs for individual communities or census tracts cannot be directly compared to one another. This is because the age distribution of a community has a strong effect on the number of expected diagnoses, and no two communities have the same age distributions within their populations. Comparisons of the SIRs for two communities would be valid only if there were no differences in the age and sex distributions of the two communities’ populations.

The table below summarizes the differences between a direct age-adjusted incidence rate and an indirect age-adjusted incidence rate (SIR).

Type of rate

Direct Incidence Rate

Standardized Incidence Ratio (SIR)

Calculation

Statewide or county age-specific cancer rate applied to US 2000 Standard Population

Massachusetts age- and gender-specific cancer rates applied to local (i.e., community or census tract) population

Geographic Areas

Counties, statewide

Census tracts, communities, counties, EP Regions and EOHHS regions

How to use

Can compare cancer rate in one county to that of another across Massachusetts and across multiple states.

Comparison is made possible because all rates have been standardized or applied to the same large population
(i.e., US 2000 Standard Population).

Not appropriate for small areas (census tracts, communities) due to instability of small population numbers. For census tracts and communities, use (SIR).

Can compare cancer incidence in each community (or census tract) to Massachusetts as a whole. However, cannot compare the SIR of one community (or census tract) to that of another.

Communities are not directly comparable to each other unless they have the exact same age/gender compositions.

Direct Incidence Rates for Cancer

Cancer incidence is the number of new cancer diagnoses in a defined population over a specific time period. A direct incidence rate is the most appropriate statistic to compare cancer incidence in one relatively large area to another relatively large area (such as one county to another or one state to another). For example, direct age-adjusted incidence rates might be used to determine whether prostate cancer occurred more frequently in Suffolk County vs. Norfolk County. The MA EPHT website reports direct rates for Massachusetts at the county and statewide levels.

All direct rates are age-adjusted because cancers do not impact different age groups equally.

Example: Age adjustment

Prostate cancer is more common among older men. A county containing 10,000 men over the age of 50 would naturally have more prostate cancer diagnoses than a county containing only 2,000 men over 50. In order to accurately compare prostate cancer in these two counties, we must adjust for their different age structures.

Example: Comparing direct rates between two counties

Let's say a county had a direct age-adjusted rate of 9.4 for prostate cancer and another county had a rate of 8.0. This would mean that prostate cancer occurred at a rate of 9.4 cancer diagnoses per 100,000 people over a 5-year time period in the first county, and at a rate of 8.0 cancer diagnoses per 100,000 people over the same 5-year period for the second county. Since we have accounted for the different age structures of the counties, we can compare the two rates and conclude that the first county had a higher rate of prostate cancer during this time period than the second county.

For more information on direct incidence rates for cancer, see the FAQ.

One calculation will generate:

  • The number of diagnoses

  • An age-adjusted cancer incidence rate
Sample cancer incidence table
Data Considerations

When reviewing and interpreting cancer data, it is important to consider the following:

  • Direct rates have been adjusted for different age distributions and are directly comparable between two geographic areas.
  • Counts and rates are calculated based upon residential address at the time of diagnosis. No information is available on prior residences.
  • To protect privacy, no information is shown that could identify an individual. Data suppression rules govern the release of small case counts.
  • MA EPHT incorporates the use of the Relative Standard Error (RSE) when assessing statistical stability. The RSE provides a measure of reliability. When the RSE is greater than 30%, the rate is unstable and caution should be exercised when interpreting results.
  • Numbers and rates may differ slightly from those contained in other publications. These differences may be due to file updates, differences in calculation methods (such as grouping ages differently or rounding off numbers at different points in calculations), and updates or differences in population estimates.

For additional information, please read the FAQ.

Available Data on Cancer Direct Rates

Click the  Explore Data link on the right toolbar to access the following measures. The most current available data will be shown. Be sure to check the site periodically for new data as it becomes available. Direct rates are presented by county or statewide for individuals of all ages for 15 types of cancer as well as two leukemia subtypes (acute myeloid leukemia and chronic lymphocytic leukemia).

  • Direct rates are presented for childhood cancers for two age groups (0-15 and 0-19 years of age) for cancers of the brain and central nervous system as well as for leukemia and two subtypes of leukemia (acute lymphoid leukemia and acute myeloid leukemia).
  • Annual rates are available on a statewide level. Average 5-year rates are available at the county and state levels. Due to small numbers, only 5-year average rates are presented for childhood cancers at the state level.

Standardized Incidence Ratios for Cancer

Sample map of a Cancer SIR being displayed

standardized incidence ratio (SIR) is the most appropriate statistic to examine cancer incidence in a small area, such as a community or a census tract. For example, an SIR might be used to determine whether prostate cancer occurred more frequently than expected in Boston, compared to Massachusetts as a whole.

An SIR is the ratio of observed cancer diagnoses in an area to the number of expected diagnoses multiplied by 100. The expected number is based on the statewide cancer experience.

Comparison of SIRs between communities or census tracts is an inappropriate use of the statistic. Such comparisons are inappropriate because the age distribution or structure of a community has a strong effect on its cancer rates, and no two communities have the same age distributions within their populations. Comparisons of the SIRs for two communities would be valid only if there were no differences in the age and sex distributions of the two communities’ populations. An SIR can appropriately be used to evaluate whether the cancer incidence of a community or census tract differs from that of the state as a whole.

Example: Interpreting an SIR

Let us say that Community A has an SIR of 200 for prostate cancer during 2000-2004, while Community B has an SIR of 100 for that same cancer during that same period. In this case, it would be accurate to say that in Community A, prostate cancer is roughly twice as common as expected compared to Massachusetts as a whole, while in Community B, it is about as expected compared to Massachusetts as a whole. The “expected” number of cancers refers to the number of diagnoses that would be expected in that community based on the age adjusted cancer rate in Massachusetts as a whole. However, it would not be accurate to say that in Community A, prostate cancer is twice as common as in Community B. Again, this is because Community A and Community B do not have comparable age distributions, and prostate cancer is strongly affected by age.

For more information on direct incidence rates for cancer, see the FAQ.

One calculation will generate:

  • An observed number of diagnoses
  • An expected number of diagnoses
  • An SIR
  • A 95% Confidence Interval
Sample cancer incidence table
Data Considerations

When reviewing and interpreting Cancer data, it is important to take into consideration the following:

  • Comparison of SIRs between communities or census tracts is not possible because each of these areas has different population characteristics.
  • Counts and rates are calculated based upon residential address at the time of diagnosis. No information is available on prior residences.
  • To protect privacy, no information is shown that could identify an individual. Data suppression rules govern the release of small case counts.
  • Statistical significance for SIRs is assessed to determine if the observed number of diagnoses is statistically significantly different from the expected number of cancer diagnoses (based on the statewide experience), or if the difference may be due solely to chance. Statistical significance is determined by the 95% confidence interval.
  • MA EPHT incorporates the use of the Relative Standard Error (RSE) when assessing statistical stability. The RSE provides a measure of reliability. When the RSE is greater than 30%, the rate is unstable and caution should be exercised when interpreting results.
  • Numbers and rates may differ slightly from those contained in other publications. These differences may be due to file updates, differences in calculation methods (such as grouping ages differently or rounding off numbers at different points in calculations), and updates or differences in population estimates.

For additional information, please read the FAQ.

Available Data on SIRs for Cancer

Click the Explore Data link on the right toolbar to access the following measure for cancer in your community. The most current available data will be shown. Be sure to check the site periodically for new data as it becomes available.

  • SIRs are available by sex for 23 types of cancer for individuals of all ages and 5 types of childhood cancer
  • SIRs are available for census tracts, communities, counties, Emergency Preparedness (EP) Regions, and Executive Office of Health and Human Services (EOHHS) regions

Cancer Risk Factor Summaries

A risk factor is anything that is related to a person's chance of developing cancer. Some risk factors can be controlled while others cannot. Risk factors include hereditary conditions, medical conditions or treatments, infections, lifestyle factors, or environmental exposures.

Did You Know?

Approximately 9% of all cancer deaths are thought to be related to environmental or occupational exposures.
Pie chart of primary causes of estimated cancer deaths

Different cancers have different risk factors. For example, excess exposure to sunlight is a risk factor for skin cancer; oral tobacco use is a risk factor for mouth, throat, and many other cancers. Although risk factors can influence the development of cancers, most do not directly cause cancer. An individual's risk of developing cancer may change over time due to many factors and it is likely that multiple risk factors influence the development of most cancers.

The risk factor summaries on this page are designed to serve as a general fact sheet. For more information on other possible risk factors and health effects being researched, please visit the American Cancer Society website. Knowing the risk factors that apply to specific cancers and discussing them with your health care provider can help in making more informed lifestyle and health care decisions.

Check back periodically as new information is added to this page.

Cancer Risk Factor Summaries
Bladder
Bone
Brain & Other Nervous Systems (ONS)
Breast
Hodgkin Disease
Kidney and Renal Pelvis
Leukemia
- Acute Lymphocytic Leukemia (ALL)
- Acute Myeloid Leukemia (AML)
- Chronic Lymphocytic Leukemia (CLL)
- Chronic Myeloid Leukemia (CML)
Liver and Intrahepatic Bile Duct (IBD)
Lung and Bronchus
Mesothelioma
Multiple Myeloma
Non-Hodgkin Lymphoma (NHL)
Thyroid

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