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Breast cancer is rare in men. In California, during the five-year period 1988-1992, only 546, or less than 0.2% of the 295,466 invasive cancers diagnosed among men, originated in the breast (1). Among the 86,142 invasive breast cancers diagnosed in men and women during that time, 0.6% were in men. During the same period of time, 112 California men died from breast cancer, less than 0.1% of all male cancer-related deaths.
The 1988-1992 average annual age-adjusted incidence rate of male breast cancer was 0.8 per 100,000, and the mortality rate 0.2 per 100,000. These rates are similar to incidence and mortality data from the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) Program, which, for the same time period, reported male breast cancer incidence and mortality rates of 0.9 and 0.2, respectively (2). SEER incidence rates are based on approximately 10% of the U.S. population; the mortality rates are nationwide.
Breast cancer in men is histologically and clinically similar to the disease in women (3,4), with the very large difference in incidence being due to the relatively small number of breast cells in men and different hormonal stimuli. Survival is also similar for men and women when matched for age and stage at diagnosis (5). However the overall prognosis is poorer because men usually present at a later stage, with a higher frequency of lymph node involvement. This has been linked to the anatomical differences between male and female breasts, particularly differences in the lymphatic drainage.
Variations by nationality, ethnicity, and religion are similar for males and females (3); incidence is relatively low in Japan and Finland, and relatively high in North America and Great Britain (4), and Jewish men as well as Jewish women have an increased relative risk compared to other religious groups (3). Differences between the sexes include the strong association with high socioeconomic status seen in women but not in men (3), and a higher proportion of male than female carcinomas having estrogen receptors (6).
Some of the same risk factors found in women have also been reported in men, particularly family history (3), some of which is associated with recently identified breast cancer susceptibility genes, particularly BRCA2 (7); ionizing radiation (8) and a history of benign breast disease (which in men includes gynecomastia) (9) also have been shown to increase risk in men as well as in women. Hormonal factors specific to men that have been associated with male breast cancer include cryptorchidism, Klinefelter's syndrome, a history of mumps in adulthood, and infertility (9), conditions likely to be associated with a relative deficiency of androgens. One case-control study showed a higher risk, possibly through an increase in the production of endogenous estrogens, in men who were heavier than controls at age 30 (10), and several breast cancers have been reported in transsexuals taking estrogens (4). Other reported risk factors (3,10,11) include prior tuberculosis, liver disease, a history of diabetes, use of amphetamines (which have been reported to cause gynecomastia), and therapeutic use of digitalis. As in women, cigarette smoking and caffeinated beverages have not been found to increase the risk of breast cancer in men (12). Alcohol, which has been associated, with an increased risk of female breast cancer in some studies, has not been shown to be a risk factor for male breast cancer (12).
Certain of the occupations and industries for which an elevated male breast cancer risk has been reported may have been associated with exposures that could affect hormonal balance. These include blast furnaces and steel mills, which entail exposures to high temperatures that could damage the testes (11,12), and, in Sweden, the soap and perfume industry, which at one time included the manufacture of estrogen-containing creams (13). Additionally, a case-control study of French and Swiss male breast cancer cases showed a statistically significant elevation in risk for butchers, although the numbers were small (11). The hypothesis was that butchers may have been exposed to high levels of estrogens from the use of growth promoters in meat and poultry, because butchers may tend to eat more meat than other men. Although the carcinogenic effects of electromagnetic radiation are highly controversial, data from several studies support an association between electromagnetic radiation and male breast cancer, possibly through inhibition of the pineal gland hormone, melatonin (14). These studies have shown an elevated risk among men working in jobs with potential exposure to electromagnetic fields, such as electricians, telephone linemen, electric power workers, and radio and communications workers. A significantly elevated risk was also found in the newspaper printing industry in Sweden (13). However, all of the increased risks found for various occupations and industries have been relatively small, so that even if they are substantiated, they would account for only a small fraction of male breast cancer cases.
Table 9.1 shows incidence and mortality counts and age-adjusted rates for male breast cancers in California by single year from 1988 to 1992, as well as for the total five-year period, age-adjusted to both the U.S. and the World standard populations. The small fluctuations show that there has been no real change during that time period. SEER annual incidence and mortality rates between 1973 and 1991 have also shown little change: incidence has fluctuated between 1.0 and 0.7, and mortality between 0.3 and 0.2, per 100,000 (2).
The five-year age-specific incidence and mortality rates shown in Table 9.2 and Figure 9.1 illustrate the low frequency of breast cancer among men under 35; only five cases occurred in California in that age group between 1988 and 1992. After age 35, age-specific rates increased gradually but steadily, from 0.2 per 100,000 in the 35-39 year age group to 10.0 in the 80-84 year age group, then fell to 6.0 for ages 85 and over. Mortality rates rose from 0.1 per 100,000 in the age group 45-49 to 2.6 per 100,000 for ages 85 and over.
Table 9.3 shows male breast cancer incidence and mortality counts and average annual age-adjusted rates for all races combined and for the four largest race/ethnicity groups, Asians/Others, blacks, Hispanics, and non-Hispanic whites. Variations in incidence rates among men by race/ethnicity partly followed the pattern seen among women, in that Asian/Other and Hispanic men had substantially lower rates than both black and white men (Figure 9.2), although the numbers were too small for differences in the race-specific rates to be statistically significant. However, in contrast to breast cancer incidence among women, which was considerably lower among black than among white women, male breast cancer incidence rates were similar in the two groups: black men had an incidence of 1.0 per 100,000 compared to 0.9 per 100,000 in white men. SEER data show higher age-adjusted incidence rates for black men, 1.4 per 100,000, than for white men, 0.9 per 100,000 (2).
The differences in male and female incidence by race/ethnicity can be seen in Table 9.4, which shows female and male age-adjusted incidence rates and their ratio by race/ethnicity. For all races combined, the rate for females was 107 per 100,000, the rate for males 0.8, producing a female/male ratio of 134, that is, overall, females were more than 130 times as likely to develop breast cancer as males. The ratio was highest among Hispanics, 138, and lowest among blacks, 99. Given the small numbers on which male breast cancer rates were based, the only substantial difference from the all races ratio was the lower ratio among blacks.
Age-adjusted incidence for two age groups, under 65 and 65 and over, is shown by race/ethnicity in Table 9.5 and Figure 9.3. Again, the numbers of cases on which the rates are based were too small for the differences between the racial groups to be statistically significant, but the incidence rate for the under 65 age group was higher among blacks than among whites, which is also seen in SEER data (2). Similarly, the median age at diagnosis of invasive cases (Table 9.6) was 60 among black men and 68 among white men. The higher incidence among younger black men is clearly seen in Table 9.7, which shows average annual age- and race-specific rates. Again, the number of cases was very small, but black men had the highest breast cancer rates through age group 60-64, after which the rates fluctuated.
Unlike most previous reports in which breast carcinomas in men occurred slightly more frequently in the left breast (5,9), the numbers for all races combined in California were almost evenly split between left and right. This was true for Asians/Others, Hispanics, and whites. Among black men however, 60% (24 out of 40), were right-sided (data not shown).
Table 9.8 shows the distribution of the stage at diagnosis of breast cancer by race/ethnicity for males and females. Although the numbers of cases were too small for any firm conclusions about relative proportions or racial differences in stage at diagnosis among men, the proportion of in situ cases among men of all races, 6.7%, was lower than the 10.8% of in situ cases found in a study of male breast cancer cases from SEER registries from 1983 to 1986 (6). There was no difference in the distribution of stage at diagnosis between men under and over age 65 (data not shown).
White men had the lowest percentage of in situ cases and the highest percentage of localized cases, while black men had the lowest percentage of regional cases and the highest percentage of remote cases. The percentages of "early" cases (in situ plus localized), versus "late" cases (regional plus remote) were similar across races, except that Asian/Other men had a slightly lower percentage of early cases (48%), than black, Hispanic, or white men (53%, 51%, and 54% respectively).
As has been reported in other series (5), when differences in stage at diagnosis were examined by sex (Figure 9.4), a smaller proportion of men than women were diagnosed at an early stage. In addition to the anatomical differences between male and female breasts, increased awareness of the disease and breast cancer screening among women may have contributed to this difference. The smallest differences in both early and late stage diagnoses were between black men and women (black women had the lowest percentage of early stage cases). Among whites and Asians/Others, in situ percentages were substantially lower in men than in women.
Stage at diagnosis was specified in 519 out of the total of 546 invasive male breast cancers. Of these 519 cases, 52.6% were localized, 40.1% regional, and 7.3% remote. These percentages were very similar to the comparable percentages in the study of SEER cases, 54.6 localized, 42.7 regional and 2.6 remote (5), except for a higher percentage of remote cases among California men.
Table 9.9 and Table 9.10 show counts and percentages of the histological distribution of invasive and in situ male breast cancer cases, respectively. Of the 536 microscopically confirmed invasive cases, 530 (98.9%) were carcinomas. The histologic distribution was very similar to the distribution found in SEER data, both during the five-year period 1983-87 (15), and during the fifteen years 1973 to 1987 (16). Over three-quarters (76.7%) were infiltrating ductal carcinomas, a little higher than the percentage in California women (71.6%). Other than carcinoma and adenocarcinoma not otherwise specified, the next most frequent groups were papillary adenocarcinomas, 3.5%, and Paget's disease, 1.7%, both also higher than the percentages in women (0.6% and 0.9%, respectively). Both lobular carcinoma (0.4%) and infiltrating duct and lobular carcinoma (0.4%) were much less frequent than in women (7.2 and 4.5%, respectively), as would be expected, since male breasts do not usually contain lobules. Mucinous adenocarcinomas (0.6%), comedocarcinomas (0.2%), and medullary carcinomas (0.4%), were also lower in men than in women. Of the in situ cases, 59% were non-infiltrating intraductal carcinomas, similar to the percentage in women, 55.2%. The proportion of papillary adenocarcinomas in situ was higher in men than in women, 33.3% vs. 5.4%.
Table 9.11 shows surgical treatment for male breast cancer by stage (in situ, localized, and regional/remote) for the 558 cases with known stage at diagnosis. Mastectomies (mainly modified radical) were done on 74% of the in situ cases, 89% of the localized cases, and 87% of the regional/remote cases. A total of 41 cases (15% of the in situ, 7% of the localized, and 3% of the regional/remote cases) had breast conserving surgery, i.e., lumpectomy or partial mastectomy, and 25 cases had no surgery.
Male breast cancer is rare. Only 585 cases, 39 in situ and 546 invasive, were diagnosed in California men during the five years, 1988-1992, while 112 men died of the disease. California's incidence and mortality rates were similar to the rates reported by the SEER Program for the same time period.
Variations by race/ethnicity partly followed the pattern seen in women, in that Asian/Other and Hispanic men had a lower risk of developing breast cancer than either black or white men. Black and white men had almost the same age-adjusted incidence rates (1.0 vs. 0.9 per 100,000), but black men under age 65 had a higher incidence than white men, a finding also reported by SEER. Median age at diagnosis in California was 60 among black men, compared to 68 among white men.
The percentage of in situ breast cancers among California men, 6.7%, was lower than the percentage among California women, 11.8%, and lower than the 10.8% reported in a study of 1983 to 1986 cases from SEER registries.
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