Risk Factors

Many risk factors for breast cancer are known. The risk of breast cancer increases sharply after age 30. The risk of breast cancer is increased when close relatives have had breast cancer, particularly a first degree relative such as a mother or sister. The risk is even higher if the first degree relative with breast cancer was premenopausal and had bilateral breast cancer (breast cancer in both breasts). Some breast cancers in women with a family history may be the result of a specific inherited gene (or genetic trait). Within the past few years, two breast cancer genes have been discovered, BRCA-1 and BRCA-2; mutation of either of these genes is believed to increase susceptibility to breast cancer. Other breast cancers with a family history may be because of lifestyle similarities or the inheritance of certain other risk factors such as menstrual patterns and obesity.

Women who have had cancer in one breast have a higher risk of developing a second cancer. Women with ovarian or endometrial cancer also are at higher risk for breast cancer. Women with benign fibrocystic breast disease confirmed by biopsy are at higher risk of breast cancer. Several studies suggest that the increased risk associated with benign breast disease may be mostly among women with atypical hyperplasia (an abnormal increase in the number of cells in a specific area of the body such as the lining of the breast ducts).

Early age at the onset of menstruation and late age at menopause are risk factors for breast cancer. Menopause induced by the removal of the ovaries before age 40 reduces the risk of breast cancer. Never having children or having the first live birth at a late age are associated with an increased risk of breast cancer. The risk of breast cancer is higher among women of higher socio- economic status. This appears to be explained largely by the reproductive risk factors.

Large doses of radiation have been associated with breast cancer in women exposed to atomic bomb fallout at Hiroshima and Nagasaki. Women who were exposed to large doses of x-rays as part of the treatment for tuberculosis from 1935 to 1954 had a high incidence of breast cancer. The much lower doses of radiation used today for chest x-rays or mammograms are considered to be of little or no risk. (The benefits of mammography at intervals recommended by the American Cancer Society far outweigh any risk.)

Recent studies have found an increase in breast cancer risk among women who have three or more alcoholic drinks a day, compared to non-drinkers. Breast cancer risk increases with weight and body mass among postmenstrual women. A few studies found a small increase in breast cancer risk among women with high fat diets. However, more recent large studies have not found an association between fat intake and breast cancer.⁵

Long-term exposure to postmenopausal estrogen replacement therapy may increase the risk of breast cancer. Most studies have not found an association between oral contraceptive use and breast cancer. However, some recent studies suggest a possible increase in breast cancer before age 45 among women who used oral contraceptives for a long time or who started oral contraceptive use at an early age.⁵

The above risk factors partly explain the incidence of breast cancer among women.⁹ Pesticides and other chemicals that mimic or modify the action of estrogens are currently under study by various research organizations. Also under study are a diet high in fat, physical inactivity, hormone replacement therapy, genetic factors, and gene-environmental interactions.

The causes of male breast cancer are not well understood. Some factors thought to increase the risk of male breast cancer are excess weight in young adulthood, gynecomastia (abnormal swelling of the breasts), Klinefelter's syndrome (an extra X chromosome), and undescended testes; all possibly related to higher levels of estrogen. Men with a family history of breast cancer, especially a female relative who developed breast cancer before age 45, are at higher risk of breast cancer. High doses of ionizing radiation also can cause male breast cancer. It is thought that the lower estrogen levels in men compared to women may partially explain the much lower rate of breast cancer in men compared to women.

Prevention and Control

Given the known risk factors for breast cancer, opportunities for prevention are limited. The following should be studied further to see if they reduce the risk of breast cancer: moderate physical activity, a diet low in fat and high in fiber, weight control (particularly in women after menopause), and limited consumption of alcoholic beverages. A study of the use of tamoxifen, a drug that is prescribed to prevent recurrence of breast cancer, indicates that tamoxifen may prevent breast cancer in high risk women. However, there is concern that tamoxifen may have serious short- and long-term side effects. Other medications which may have similar benefits but are less hazardous are under study.

For now, early detection and treatment are the best means to increase survival and reduce mortality due to breast cancer. Mammography, breast examination by a nurse or physician, and breast self-examination are all methods to detect breast cancer early. Mammography is especially important because it can detect early breast cancers that even very skilled health practitioners may miss. Appendix I contains recommendations from the American Cancer Society for women about using these methods of early detection. Appendix II has information on the New Jersey Breast and Cervical Cancer Control Initiative which provides for free screening for eligible women in New Jersey.

Incidence and Mortality in the U.S.

Breast cancer is the most common type of cancer among women in the U.S., accounting for 30 percent of the newly diagnosed cases of cancer among women each year. About 178,700 new cases are estimated for 1998 in the U.S. Approximately one in eight women in the U.S. will have breast cancer at some time in her life, according to the American Cancer Society. The age-adjusted incidence rate of breast cancer among women in the U.S. steadily increased between 1940 and 1987, especially between 1982 and 1987, but has stabilized since 1987 at about 110 newly diagnosed cases per 100,000 women a year. Many researchers believe that some of the increase in breast cancer incidence since 1940 may be due to an increase in the proportion of women who have known risk factors for breast cancer, such as giving birth to the first child later in life and having fewer children. Another possible reason for the increase in the incidence of breast cancer, especially from 1982 to 1987, is that more women are using breast cancer screening methods such as mammography that identify breast cancer early. Thus, breast cancers that would have been diagnosed in later years (after 1982-1987) were diagnosed earlier. Breast cancer is rare among men; about 1,600 new cases of breast cancer in men are estimated to occur in 1998 in the United States, representing 0.25 percent of the total estimated cancers in men.

Breast cancer is the second most common cause of death due to cancer in women in the U.S. (lung cancer has recently become the most common) with 43,500 deaths estimated nationwide for 1998. The mortality rate of breast cancer among women is declining. The reasons for the decline are believed to include earlier detection which enables more successful treatment. The five-year relative survival rate for localized breast cancer is 97 percent, for regionally spread breast cancer it is 76 percent, and for women with distant metastases it is 21 percent.

Incidence in New Jersey - 1986-1996

Tables 10 through 12 present breast cancer incidence data by county for 1986 through 1996. Figure 6 shows statewide trends in breast cancer. Statewide, the breast cancer incidence rates were higher in white women than black women and were much higher in white and black women than in white or black men, who had similar rates (see Figure 6). This pattern held for most counties. In Hunterdon and Warren counties, black women had higher rates than white women (see Table 12), but these rates for black women may be unstable and should be interpreted cautiously because they were based on small numbers of women with breast cancer. Statewide, the breast cancer incidence rate steadily declined for white women from 1992 through 1996, but did not decline as consistently for black women (see Figure 6). The breast cancer rates for men changed little over the eleven-year time period.

Conclusion

The most important public health activity related to breast cancer at this time is screening to detect it early when the chances for survival are high. Research to uncover risk factors that are now unknown may provide additional opportunities for preventing breast cancer. In the meantime, moderate physical activity, a diet low in fat and high in fiber, weight control (particularly in women after menopause), and limited consumption of alcoholic beverages may reduce the risk of breast cancer.

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COUNTY	1986		1987		1988		1989		1990		1991		1992		1993		1994		1995		1996 (Prelim.)
	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate
Atlantic	112	90.1	137	110.2	139	112.6	156	124.4	146	113.5	150	110.2	148	113.2	139	103.9	149	122.9	154	119.2	134	106.6
Bergen	643	110.5	699	120.7	710	124.5	736	129.8	703	123.4	692	124.0	746	132.2	761	135.1	674	119.4	643	111.3	649	115.8
Burlington	204	109.2	197	104.1	241	122.1	226	114.8	217	106.8	255	126.9	246	122.7	244	120.9	264	132.0	238	113.2	242	117.7
Camden	277	107.3	281	106.1	336	130.9	317	120.9	332	127.1	336	131.8	282	107.6	288	110.8	301	117.9	276	105.7	235	87.8
Cape May	80	99.0	87	108.3	76	110.8	80	115.3	102	143.6	84	109.7	83	110.6	85	109.3	92	118.8	94	115.8	78	93.3
Cumberland	71	90.5	67	91.1	76	98.4	57	70.5	100	128.9	86	108.5	98	126.1	82	109.2	75	99.2	76	99.3	95	130.1
Essex	368	101.1	424	119.5	440	126.8	430	128.7	430	131.8	423	135.5	420	130.4	372	118.5	379	123.0	336	114.1	344	114.8
Gloucester	138	132.9	136	127.7	127	112.3	146	126.8	136	116.9	143	118.9	154	126.4	132	109.1	149	121.6	136	113.2	106	82.6
Hudson	325	102.0	302	97.0	345	111.3	269	90.0	298	95.1	260	87.6	272	90.7	296	98.7	267	91.2	259	85.7	268	91.2
Hunterdon	67	122.5	68	124.7	66	119.2	68	112.6	85	138.6	75	128.1	100	167.0	74	113.9	78	124.6	79	129.4	92	138.4
Mercer	204	112.2	193	112.6	211	123.9	202	116.8	237	132.5	217	124.9	207	116.7	254	144.2	214	121.3	217	121.9	216	125.4
Middlesex	386	111.6	412	116.6	443	121.8	401	108.5	406	110.1	412	111.5	445	119.8	487	132.2	438	116.3	438	116.4	414	108.1
Monmouth	401	127.7	416	128.2	403	123.5	401	121.6	426	129.2	408	126.0	451	130.9	424	124.2	390	116.7	413	119.5	397	113.4
Morris	260	109.4	305	129.4	294	120.9	304	124.9	308	127.4	286	115.6	324	130.5	313	126.3	318	122.8	316	126.5	310	119.4
Ocean	385	112.7	419	119.3	433	124.8	398	105.7	464	118.7	465	121.5	459	120.0	413	104.8	464	116.6	471	117.8	438	114.2
Passaic	285	109.7	296	111.2	296	110.8	277	105.1	308	120.3	266	105.5	293	114.6	251	98.5	266	100.1	271	107.9	293	117.7
Salem	44	109.7	29	78.5	36	92.9	44	113.2	41	104.6	43	110.2	55	143.6	40	106.4	40	103.7	31	79.1	49	121.8
Somerset	139	111.4	158	123.8	176	134.3	144	109.6	140	103.2	176	129.2	130	92.9	161	112.9	148	104.2	165	112.9	158	103.3
Sussex	88	139.3	80	128.1	89	138.5	69	107.0	65	96.7	86	132.4	78	115.5	86	116.3	63	89.6	85	119.4	102	148.4
Union	317	102.3	391	127.3	359	115.1	366	121.2	383	129.7	341	110.7	335	112.0	316	104.9	335	110.3	336	111.0	326	112.0
Warren	63	112.5	88	145.0	106	189.7	69	121.3	57	94.4	84	144.1	67	110.9	73	127.6	69	116.6	76	122.2	68	109.1
STATE	4860	109.9	5188	116.9	5408	121.6	5164	116.1	5387	120.0	5291	119.0	5394	119.6	5293	117.8	5175	114.8	5112	112.8	5014	110.4

¹Incidence rates - per 100,000 females, age-adjusted to the 1970 U.S. standard population. Cases of unknown county are included in the State numbers and rates. Source: New Jersey State Cancer Registry.

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COUNTY	1986		1987		1988		1989		1990		1991		1992		1993		1994		1995		1996 (Prelim.)
	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate	No.	Rate
Atlantic	14	67.2	24	111.2	22	105.7	26	114.2	17	70.1	17	79.5	35	148.7	17	73.7	26	99.8	25	90.6	26	91.0
Bergen	19	90.6	19	87.2	18	76.8	21	88.6	18	76.8	18	69.6	30	123.4	15	59.8	21	74.9	32	116.2	22	76.5
Burlington	17	89.9	26	129.0	31	146.6	23	95.6	30	127.4	28	107.4	31	130.0	24	89.3	15	52.9	21	77.7	26	100.2
Camden	34	93.8	34	93.6	47	128.9	32	79.6	37	92.2	42	106.2	43	105.2	42	100.9	45	103.0	44	96.1	38	85.3
Cumberland	7	75.9	6	61.0	5	54.8	9	94.1	6	53.2	---	---	15	125.3	9	79.8	10	78.5	10	95.3	13	114.1
Essex	130	81.8	150	92.7	146	89.6	173	107.1	153	91.8	155	94.2	172	100.6	169	99.7	137	80.2	158	89.2	154	87.7
Gloucester	10	102.3	5	45.7	10	97.9	6	55.5	17	136.4	9	66.6	19	155.4	9	67.5	12	88.6	19	126.5	17	127.3
Hudson	25	74.8	36	104.8	27	76.1	36	104.0	32	90.1	38	108.1	37	98.8	38	98.2	18	42.7	26	68.7	39	97.5
Mercer	38	134.9	23	84.5	28	93.4	32	104.8	24	77.6	49	150.3	27	82.7	41	126.1	40	116.8	51	148.6	31	85.5
Middlesex	17	83.5	23	115.6	19	95.5	14	61.1	17	76.6	24	106.7	15	61.6	25	108.5	33	114.6	30	111.1	29	106.4
Monmouth	19	77.7	20	78.9	24	94.1	24	94.0	24	90.5	22	75.9	18	60.8	21	71.4	33	108.0	29	91.2	22	65.4
Morris	---	---	5	62.6	---	---	7	106.5	8	136.9	---	---	7	95.4	---	---	12	152.9	6	61.1	---	---
Ocean	---	---	---	---	7	139.6	5	97.2	---	---	6	108.1	7	129.6	5	88.3	---	---	---	---	11	152.5
Passaic	21	72.2	19	63.3	20	67.0	28	100.3	19	61.3	27	76.6	19	58.5	23	66.7	31	81.8	30	81.2	37	91.7
Salem	---	---	5	97.9	---	---	---	---	5	99.7	---	---	12	202.1	7	96.7	---	---	6	106.4	7	96.4
Somerset	---	---	---	---	5	64.2	5	65.5	6	99.2	8	122.6	8	110.7	9	98.8	5	51.7	8	104.2	7	57.4
Union	43	95.2	53	112.1	52	110.7	52	111.4	63	133.3	53	106.2	50	104.3	47	90.9	61	114.7	51	95.1	41	75.3
STATE	413	85.7	457	93.0	472	93.3	497	97.9	490	94.1	504	94.9	554	101.6	508	91.6	513	88.7	556	94.3	526	88.0

¹Incidence rates - per 100,000 females, age-adjusted to the 1970 U.S. standard population. Source: Cases of unknown county are included in the State numbers and rates. Counties with six or more years of fewer than five cases each year were removed from the table - Cape May, Hunterdon, Sussex, and Warren counties. The dashes indicate fewer than five cases. New Jersey State Cancer Registry.

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COUNTY	MALE				FEMALE
	WHITE		BLACK		WHITE		BLACK
	Number	Rate2	Number	Rate2	Number	Rate2	Number	Rate2
Atlantic	16	1.3	---	---	1564	112.0	249	95.2
Bergen	81	1.6	---	---	7656	122.3	233	85.7
Burlington	21	1.3	---	---	2574	117.0	272	102.8
Camden	25	1.1	---	---	3261	113.9	438	98.5
Cape May	10	1.2	---	---	941	112.2	30	79.3
Cumberland	11	1.7	---	---	883	104.7	93	79.2
Essex	39	1.4	16	1.4	4366	121.8	1697	92.2
Gloucester	10	1.0	---	---	1503	116.8	133	99.2
Hudson	31	1.2	---	---	3161	94.6	352	87.4
Hunterdon	---	--	---	---	852	128.8	15	210.2
Mercer	15	1.0	---	---	2372	123.3	384	109.9
Middlesex	38	1.2	---	---	4682	115.9	246	95.7
Monmouth	31	1.1	---	---	4530	123.8	256	82.6
Morris	28	1.3	---	---	3338	122.8	60	77.0
Ocean	45	1.3	---	---	4809	116.2	56	89.7
Passaic	24	1.0	---	---	3102	109.3	274	75.1
Salem	6	1.8	---	---	452	105.5	57	89.9
Somerset	14	1.1	---	---	1695	112.2	65	79.2
Sussex	9	1.6	---	---	891	120.7	---	---
Union	28	1.0	---	---	3805	114.4	566	104.0
Warren	---	---	---	---	820	125.8	10	129.5
STATE	488	1.2	46	1.1	57286	116.2	5490	93.0

¹Incidence rates - per 100,000 population, age-adjusted to the 1970 U.S. standard population. Cases of unknown county are included in the State numbers and rates. The dashes indicate fewer than five cases. Source: New Jersey State Cancer Registry.
²Average annual rate.