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Last Edited: 8/11/2010

Cancer: Measurement and Limitations

To understand the overall burden of cancer in the population, it is important to monitor newly diagnosed cancer cases (incidence), as well as cancer deaths (mortality).  Here, we provide the counts and rates of newly diagnosed cases for a select group of cancers

This section contains the following topics:


CANCER CLASSIFICATION

Cancer categories were defined using the International Classification of Disease for Oncology, Third Edition, 2000 (ICD-O-3):

Adult cancers:

Cancer Type

ICD-O-3 Codes Used

Lung and bronchus

C340:C349 (Excl. M-9050-9055, 9140, 9590:9989)

Female breast

C500:C509 (Excl. M-9050:9055, 9140, 9590:9989)

Bladder (including in situ)

C670:C679 (Excl. M-9050:9055, 9140, 9590:9989)

Brain and other nervous system (ONS)

C710:C719 (Excl. M-9050:9055, 9140, 9530:9539, 9590:9989)

Thyroid

C739 (Excl. M-9050:9055, 9140, 9590:9989)

Non-Hodgkin lymphoma

9590:9596, 9670:9671, 9673, 9675, 9678:9680, 9684, 9687, 9689:9691, 9695, 9698:9702, 9705, 9708:9709, 9714:9719, 9727:9729 (9823, 9827), all sites except C420, C421, C424

Acute lymphocytic leukemia

9826, 9835:9837

Acute myeloid leukemia

9840, 9861, 9866, 9867, 9871:9874, 9895:9897, 9910, 9920

 

Pediatric Cancers:

Cancer Type

ICD-O-3 Codes Used

Leukemia

9800-9804, 9820-9827, 9830, 9840-9842, 9850, 9860-9864, 9866, 9867, 9868, 9870-9894 9900, 9910, 9930-9941/C00.0-C80.9

Acute myeloid leukemia

9861/C00.0-C80.9

Central Nervous System

9380 (C72.3), 9381, 9400-9441 (C00.0-C80.9), 9383, 9390-9394/(C00.0/C80.9), 9380 (C70.0-C72.2, C72.4-C72.9), 9380 (C72.3), 9381, 9400-9441 (C00.0-C80.9), 9383, 9390-9394/C00.0/C80.9, 9380 (C70.0-C72.2, C72.4-C72.9)

 

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DATA SOURCES

Cancer data

In 1985, the California Cancer Registry (CCR) was established in accordance with the California Health and Safety Code sections 103875, 103885, and 100330 to collect information on cancer cases throughout California.  CCR collects information on over 140,000 cancer cases annually.  CCR is a collaborative effort of the California Department of Public Health, regional cancer registries, and the Public Health Institute.  CCR coordinates with medical treatment facilities around the state and a network of scientists and technicians to receive cancer reports, check for accuracy, and perform analyses while following strict guidelines to protect patient privacy.  CCR operates in support of and coordination with the National Program of Cancer Registries (NPCR) at the Centers for Disease Control and Prevention and the Surveillance Epidemiology and End Results (SEER) program of the National Cancer Institute.

The information CCR collects includes demographic data, cancer type, extent of disease at diagnosis, first course of treatment, and survival. Most types of cancer are reported to the registry including all malignant neoplasms (regardless of tissue origin), malignant lymphoma, Hodgkin Disease, and leukemia.  The following cancers are not included: basal cell and squamous cell carcinoma of the skin, cervical carcinoma in situ, and grade III cervical intraepithelial neoplasia.  CCR also collects information on benign brain tumors.

 

Population data

Population (denominator) numbers are from the National Center for Health Statistics bridged population estimates, which are based on Census 2000.  Methods for these estimates can be found here.

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STATISTICAL CONCEPTS

Rates

The California Cancer Registry tabulates newly diagnosed cancers of various types that are reported to them each year. Among adults, each rate is the number of new cancer diagnoses in a population, divided by the number of people, and multiplied by 100,000. Among children, each rate is the number of new cancer diagnoses in a population, divided by the number of children in the population, and multiplied by 1,000,000.


Some counties have a greater proportion of people who are old or young than other counties, which makes it difficult to compare cancer risk between multiple counties or a single county over time. Epidemiologists use a technique called age adjustment in order to make meaningful comparisons. The rates presented here are age-adjusted rates.

Using a common method of age-adjustment, we weight rates to be comparable to a standard population.  For the age-adjusted cancer rates presented here, we use the U.S. Census 2000 population as the standard population.

 

Confidence Intervals

Given the data at hand, to understand the range of possible values for the true cancer rate, we calculate the 95% confidence interval for each rate.  The 95% confidence interval is the range of values that includes the true value 95% of the time.  Statisticians have developed a large number of methods for calculating these confidence intervals. Usually the result is the same no matter which method is used, although when numbers of events are small, the results may differ.

The method developed by Tiwari, Clegg, and Zou1, applies specifically to the situation of age-adjusted health outcomes such as cancers.  We have chosen to use this method for calculating confidence intervals for the CEHTP Portal, but it is important that users understand that others in the field may not be using the same method.

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SOME IMPORTANT LIMITATIONS WITH THE DATA

No information is available on prior residences

The California Cancer Registry calculates cancer rates based upon residential address at the time of diagnosis.  No information is available on prior residences.  Therefore, it is difficult to explore potential sources of exposure prior to cancer diagnosis.

 

Lag time between cancer diagnosis and reporting

Reporting of cancers for a specific year is considered to be largely complete approximately two years following that date. It is expected that one percent more incident cancer cases will eventually be added to those reported two years ago, taking into consideration the non-reporting of Veteran Administration hospitals (see explanation below).  Thus, the most complete count of cancer cases is at least three years old and counts and rates reported for more recent years are estimates.

 

Underreporting of cancer by the Veteran’s Health Administration Hospitals

Veteran’s Health Administration (VHA) hospitals in California stopped reporting cancer cases to the California Cancer Registry beginning in 2005. Although there is no way to know how many unreported cancer cases were diagnosed in these facilities since that time, historically VHA-reported cases have accounted for approximately 4 percent of all new male cancers reported to the CCR. Therefore, rates of new cancer diagnoses (incidence rates) for more recent years are based upon case counts that we believe to be underestimates of the true counts. It is not possible to determine to what extent any downward trends reflect this underreporting of cases versus true progress in the fight against cancer. Because of the population served by VHA facilities, historically only a very small percentage of cancers in California females have been reported from VHA facilities. Therefore, we believe the lack of reporting from these facilities will have little or no impact on the accuracy of female cancer rates for recent years.

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Reference

1. Tiwari RC, Clegg LX, and Zou Z. Efficient interval estimation for age-adjusted cancer rates. Statistical Methods in Medical Research. 2006. 15(6):547-569.