Refer to: Preston-Martin S, Menck HR: The epidemiology of thyroid cancer in Los Angeles County. West J Med 131: 369-372, Nov 1979

The Epidemiology of Thyroid Cancer in Los Angeles County SUSAN PRESTON-MARTIN, PhD, and HERMAN R. MENCK, MBA, Los Angeles

More than 300 new cases of thyroid cancer are diagnosed in Los Angeles County every year. The age-adjusted annual incidence rates of this disease for all races combined are 2.4 for males and 6.1 for females. Rates for women are more than twice rates for men in each major ethnic group. Blacks of both sexes have the lowest rates; Japanese, Chinese, other Asians and Spanishsurnamed whites all have rates that are as high as or higher than rates among non-Spanish-surnamed whites. Other demographic patterns include the excess of thyroid cancer among Jewish residents of Los Angeles. There have been an increase in thyroid cancer incidence and a decline in mortality for this disease in the United States over the past several decades. Several possible explanations can be made for these trends. Also, the risk factors for thyroid cancer deserve review. Los ANGELES is a convenient place to study the patterns of occurrence of a relatively rare type of cancer such as thyroid cancer. Although thyroid cancer accounts for only 1.4 percent of all new malignant lesions diagnosed among Los Angeles residents, the Cancer Surveillance Program (csp)1 collects reports on the more than 300 new cases diagnosed each year among the 7 million county residents. We will present information, derived from csp reports, describing the pattern of thyroid cancer occurrence in Los Angeles and will compare this pattern with those in other areas. Average age-adjusted annual incidence rates for all races combined for 1972 to 1976 in Los From the Department of Community and Family Medicine, University of Southern California School of Medicine, Los Angeles. This paper was presented by Dr. Preston-Martin at the California Medical Association Annual Scientific Session held in Los Angeles on March 10, 1979. Submitted March 26, 1979. Reprint requests to: Susan Preston-Martin, PhD, Department of Community and Family Medicine, USC School of Medicine, 2025 Zonal Avenue, Los Angeles, CA 90033.

Angeles were 6.06 in females and 2.41 in males (H. R. Menck, unpublished data, 1978), with an overall female-to-male sex ratio of 2.5:1. Los Angeles rates are similar to those reported from other areas in the United States, whose rates, like those reported for Cali, Colombia, and for Israel, are among the highest in the world.2 Figure 1, which shows Los Angeles incidence rates by race and sex, illustrates that for each major ethnic group female rates are two to seven times higher than male rates. Los Angeles blacks have the lowest rates; this finding agrees with reports of low rates for blacks in other areas of the United States.2 The rates among men and women with Spanish surnames were not significantly different from rates among other whites. The total number of cases of thyroid cancer among Asians was too small for differences to be significant, but annual age-adjusted incidence rates were uniformly higher among Asian women than among THE WESTERN JOURNAL OF MEDICINE



Incidence by Age and Sex Figure 2 shows the age curves of thyroid cancer incidence for white men and women in Los Angeles, and Figure 3 shows the female-to-male sex ratio for each age group. For the youngest age group (0 to 14 years) the female rate was more than four times the male rate. Incidence among females increased rapidly, remained high during reproductive years and declined somewhat after menopause. Incidence among males, in contrast, increased more steadily throughout life, with male rates approaching female rates in the oldest age groups. Table 1 shows the distribution of incidence by social class for males and females and the femaleto-male sex ratio for each class. The sex ratio was similar for all classes. In addition, we see no trend relating social class to incidence. Analysis of csp occupational data on white males (excluding those with Spanish-surnames), who were 20 to 64 years old in 1972 to 1974 when their tumors were diagnosed, shows that

whites without Spanish surnames: Chinese women had a rate of 7.44 and Japanese women a rate of 7.51. A total of 27 cases occurred among other nonwhite women, predominantly Filipino, Korean, Thai, Vietnamese and Samoan-an annual rate of 13.00. Chinese and Filipino women in Hawaii also had high rates-higher than those for Hawaiian whites or Hawaiian Japanese.2 ANNUAL INCIDENCE 13.0 ;


6.0 4.0




o v

(Excluding SURNAMED Spam. Sur.)

Figure 1.-Distribution of thyroid cancer cases by race, Los Angeles County, 1972 to 1976.


4(Y EA


0-.14 __ _ __: ...



.. .. ........ .:




15-24 25-304 :__ _. 14 35-4 45-514w~ ~ ~ 55-6



20.0r FEMALE

X 10.0

L. 0









..... .

......... ...... I










TABLE 1.-Frequency and Annual Age-Adjusted Incidence Rates of Thyroid Cancer by Sex and Social Class* for Whites (Excluding Spanish-Surnamed), Los Angeles County, 1972 to 1976


a 0.5 F!







Males Number Rate

Social Class



2 3 I



35 55 75+ Age at Diagnosis

Figure 2.-Thyroid cancer: Average age-specific annual incidence rates, Los Angeles County, 1972 to 1976. 370


SEX RATIO Figure 3.-Sex ratio of female to male incidence for whites (excuding Spanish surnamed) for thyroid cancer, Los Angeles County, 1972 to 1976.


o 1.0 1~



~ ~ ~~...

ALL 0:1

0 0 0



I ~~~~~~A







64-7 75








(High) ...

... .*


5 (Low) Unknown TOTAL

... .. ..





44 3.90 98 2.92 85 2.65 2.02 82 22 3.02 2 333



Females Number Rate

99 245 243 232 42

Female:Male Sex Ratio

7.07 6.35

6.41 5.01 7.14

1.8:1 2.2:1 2.4:1 2.5:1 2.4:1

861' 6.07



*Each case was assigned the social class of the census tract he resided in at the time of his thyroid cancer diagnosis. Census social class is determined by use of a weighted sum of average family income and average educational level of people over age 23.


a greater than expected number of thyroid cancer cases occurred among workers in certain occupations. These included physicians (4 observed, 0.8 expected), engineers (4 observed, 0.8 expected), salesmen (14 observed, 5.0 expected) and managers (17 observed, 9.6 expected). The number of cases in any one occupational group, however, was too small for any firm conclusions to be drawn. When we compared the distribution of religious affiliations of all thyroid cancer patients to those of all cancer patients in Los Angeles, we observed that a greater than expected number of thyroid cancer patients were Jewish. This was true for both males and females. From 1972 to 1976, a total of 75 of our male cases were Jewish (2.5 times the number expected), and 170 of our female cases were Jewish (twice the number expected). This finding agrees with a report from Israel of higher rates for Jews than for non-Jews.2 Figure 4 illustrates the distribution of thyroid cancer cases in Los Angeles by histologic type for each sex. The distributions were similar for men and women, with papillary carcinoma the most common. Other types (in order by frequency) are mixed papillary and follicular carcinoma, follicular carcinoma, medullary carcinoma and other types that include carcinoma or adenocarcinoma (not otherwise specified), giant cell carcinoma, small cell carcinoma, Hurthle cell

carcinoma, reticular cell sarcoma, squamous cell carcinoma, mucinous carcinoma, serous pap cyst, perithelial sarcoma and unspecified lymphoma.

Trends in Thyroid Cancer Occurrence In our studies we saw no trends in thyroid cancer occurrence over the course of five years, but trends are evident from other national surveys. Age-adjusted thyroid cancer mortality has decreased for whites (both male and female), but has not changed significantly for nonwhites. Thyroid cancer accounts for only 0.5 percent of all female and 0.2 percent of all male deaths from cancer.3 Unlike mortality, incidence of thyroid cancer has increased by a factor of three over the last four decades.4 How much of this difference is real is uncertain; part of it may be attributable to an increase in diagnostic efficiency. The fact that this increase has occurred only in people younger than 50 suggests that some of the increase may be attributable to radiation-induced tumors.4 Because radiation treatment of benign conditions of infancy and childhood was not common until the late 1920's, such exposure was limited to those born in the last 50 or 60 years.

Risk Factors for Thyroid Cancer Four major categories of risk factors for thyroid cancer have been discussed in some detail in a recent review paper5: genetics, thyroid dis-



(409 CASES)

(1165 CASES)


Figure 4.-Distribution of thyroid


by histologic type, Los Angeles County, 1972 to 1976. THE WESTERN JOURNAL OF MEDICINE



ease, iodine deficiency and radiation. Some cases of thyroid cancer do occur in association with recognized familial syndromes, but such cases account for only a small proportion of the total. Other cases of thyroid cancer have occurred in persons with Graves disease or Hashimoto thyroiditis, but the issue of whether these immunogenetic disorders are specific precursors for thyroid carcinoma remains unresolved. Some geographic areas known for endemic goiter had high thyroid cancer rates which declined after iodine was added to residents' diets. This relationship between goiter and thyroid cancer is not consistent around the world, however.6 By far the best substantiated of all thyroid cancer risk factors is a history of exposure to ionizing radiation. Radiation-exposed 'cohorts known to have high rates of thyroid cancer include people who received head or neck radiation treatment for benign childhood conditions, A-bomb survivors and Marshall islanders exposed to radioactive fallout.7'9 Continued observation of persons who received iodine 131 treatment as children or adolescents for thyrotoxicosis may show an increased risk in this group as well.10 Various host factors at the time of ex-

posure enhance this high risk; these include young age at exposure, high levels of thyroid stimulating hormone at exposure and gender (female)."' There is a greater incidence of thyroid cancer as doses of radiation increase, but an increment in incidence is evident for even relatively low doses.'2 REFERENCES 1. Hisserich JD, Martin SP, Henderson BE: An areawide cancer reporting network. Public Health Rep 90:15-17, 1975 2. Waterhouse J, Muir C, Correa P, et al: Cancer Incidence in Five Continents-Vol 3. Lyon, France, International Agency for Research on Cancer, 1976 3. Cancer statistics, 1976. CA 26:14-29, 1976 4. Cancer in Connecticut: Incidence and Mortality Rates 19351974. Hartford, Connecticut Tumor Registry, (In Press) 5. Schottenfeld D, Gershman ST: Epidemiology of thyroid cancer-Part III. Clin Bul 7:98-104, 1977 6. Ramalingaswami V: Iodine and thyroid cancer in man, In Hedinger CE (Ed): Thyroid Cancer. Berlin, Springer-Verlag, 1969, pp 111-123 7. Favus MJ, Schneider AV, Stachura ME, et al: Thyroid cancer occurring as a late consequence of head and neck irradiation. N Engl J Med 294:1019-1025, 1976 8. Parker LN, Belsky JL, Yamamoto T, et al: Thyroid carcinoma after exposure to atomic radiation. Ann Intern Med 80: 600-604, 1974 9. Conrad RA: A twenty-year review of medical findings in a Marshallese population accidentally exposed to radioactive fallout. Upton, New York, Brookhaven National Laboratcry, 1973 10. Hayek A, Chapman EM, Crawford JD: Long-term results of treatment of thyrotoxicosis in children and adolescents with radioactive iodine. N Engl J Med 283:949-953, Oct 29, 1970 11. Hempleman LH, Hall WJ, Phillips M, et al: Neoplasms in persons treated with X-rays in infancy: Fourth survey in 20 years. J Natl Cancer Inst 55:519-530, 1975 12. Modan B, Ron E, Werner A: Thyroid cancer following scalp irradiation. Radiology 123:741-744, 1977

Retrolental Fibroplasia IN CONTRAST to the decades of the 40's and 50's, who gets retrolental fibroplasia today? . He's the sickest baby in the nursery. He's the one who needs the most in the way of life support systems, just to keep him alive. Respiratory distress syndrome and multiple spells of apnea are two respiratory diseases, if you will, that seem to predispose to retrolental fibroplasia. .


-JOHN T. FLYNN, MD, Miami, Florida Extracted from Audio-Digest Ophthalmnology, Vol. 17, No. 5 in the Audio-Digest Foundation's subscription programs. For subscription information: 1577 E. Chevy Chase Drive, Glendale, CA 91206


NOVEMBER 1979 * 131

* 5

The epidemiology of thyroid cancer in Los Angeles county.

Refer to: Preston-Martin S, Menck HR: The epidemiology of thyroid cancer in Los Angeles County. West J Med 131: 369-372, Nov 1979 The Epidemiology of...
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