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© E.A. Mihailov, V.N. Sagaidak, E.A. Golubeva,
L.Yu. Chepumaya, 1993 УДК 618.19-006.6-055.2(470.311):313,13
E.A. Mihailov, V.N. Sagaidak, E.A. Golubeva,
L.Yu. Chepurnaya
BREAST CANCER IN NULLIPAROUS WOMEN (INTERIM REPORT)
Cancer Control Department
Many investigators point out unfavorable effect of no or few deliveries on development of breast cancer (BC) [5, 7, 10]. S. Uasa [5] and A. Schatzkin [8] emphasize the fact that childless women and mothers of few children have higher risk of BC than those who have 5 or more deliveries.
T. Draghicescu [7 ] compared the number of nullipar-ous women and women with 1—3 or 4—5 children among BC patients and normal women. She discovered that nul-liparous women and mothers of 1—3 children preponderated among the patients, while the control group showed a statistically significant predominance of women having 4—5 deliveries. Basing on results of an international investigation B. McMagon [2 ] came to the conclusion that the risk of BC in childless women is higher than in women with children. The author believes that the risk of BC occurrence is associated with the absence of deliveries rather than with other factors.
LI. Remennik [3] studied the effect of reproductive behavior on the risk of BC to consider the absence of children and small number of deliveries to be the main demographic risk factors.
We decided to study BC incidence in nulliparous women because this risk factor is often mentioned in the literature and its evaluation is unambiguous.
Since 1983 our department have been teaching women to examine themselves. The teaching is carried out at randomly chosen enterprises and institutions in Moscow. From 1984 to 1991 the teaching was performed at 144 en-
Table 1
The rate of nulliparous women in different age groups
Age, years No of women interrogated Of them had on deliveries
No of cases %
30—39 7 935 1144 (14.4%)
40—49 10 185 1078 10,6%
50—59 10 824 1245 (11.5%)
60—69 2 118 299 (H1%)
> 70 335 50 (14,9%)
Total 31405 3816 12,2
There are no data available about 8 women
Table 2
BC incidence in nulliparous women in different age groups
terprises and institutions with a coverage of 31,405 women. All women taking the self-examination courses gave epidemiological information about themselves such as the number of deliveries, abortions, time of menstruation beginning and end, etc.
All the trained (interrogated) women were followed-up for detection of BC incidence. For this purpose lists of the trained (interrogated) women were compared with BC records in Moscow. The comparison has been performed every year since 1984.
Among the 31,405 women examined there were 3,816 nulliparous women. The rate of childless women in different age groups is presented in table 1.
The nulliparous women were 12.1 % of the whole cohort. There is a statistically significant difference between the age group of 30 — 39 years and the age groups of 40 — 49 and 50 — 59 years.
In order to evaluate BC incidence among childless women we calculated the parameter of man-year for the time of follow-up in this group of women. The total number of follow-up years was 7.5.
Since the interrogatory was carried out during the whole year, one year of interrogatory was considered to be half year for all the women under study at the average.
All the 3,816 nulliparous women were under surveillance for 17,828 man-years. There were 13 cases of BC incidence during the period of surveillance. Age distribution and BC incidence in different age groups are showed in table 2. The difference in BC incidence among the age groups was not statistically significant.
We also studied the influence of family status, abortions and body weight on BC incidence in nulliparous women.
BC incidence among unmarried women was 6 times as high as in married ones: crude and standard rates of BC incidence in married and unmarried women showed a statistically significant difference (table 3). This factor seems to be of great importance in respect of cancer incidence in childless women.
The effect of abortions on BC incidence is showed in table 4. The difference in BC incidence in women with and without abortions is not statistically significant. The difference in the incidence respective of the number of abortions is not significant either. We studied BC incidence in nulliparous women depending upon the family status and abortions (table 5). As is seen married women without a history of abortions have a considerably lower risk of BC occurrence (the difference is statistically sighificant).
And finally we failed to find any association of body weight and BC incidence in childless women.
We evaluated the effect of the mentioned risk factors on BC incidence. For this purpose we calculated
Age, years No of women under surveillance No of BC occurrences No of surveillance man-years BC incidence per 100 thousand women at a 95% confidence interval
30 — 39 1144 (29,9%) 1 5217 19,2 (0,48 — 106,9)
40 — 49 1078 (28.2%) 7 5107 137,1 (54,9 — 282,4)
50 — 59 1245 (32,7%) 3 5883 51,0 (10,5 — 148,5)
60 — 69 299 (7,9%) 1 1369 73,0 (1,8 — 401,5)
> 70 50 (1,3%) 1 251 398,4 (9,9 — 2191,2)
Total 3816 100 13 17828 72,9 (38,7 — 123,9)
Family status No of women under surveillance No of surveillance man-years Incidence
No of cases per 100 thousand women
crude rate standard rate
Married 2677 13106,5 4 30,5 (8,3 — 78,1) 29,9 (8,1 — 76,5)
Unmarried 1137 4712,5 9 191,0 (87,5 — 362,9) 197,3 (90,4 — 374,9)
No data 2 9,0 — — —
Total 3816 17 828 13 72,9 (38,7 — 123,9)
Table 4
BC incidence in nulliparous women respective of the number of abortions
No of abortions No of women under surveillance No of surveillance man-years Incidence
No of cases per 100 thousand women at a 95% confidence interval
None 2593 12177,5 7 57,5 (23,0 — 118,4)
One 596 2753,0 3 108,9 (22,4 — 317,9)
Two or more 627 2897,5 3 103,5 (21,3 — 302,2)
Total 3816 17 828 13 72,9 (38,7 — 123,9)
Table 5
BC incidence in nulliparous women respective of family status and abortions
Family status Abortions No of women under surveillance No of surveillance man-years Incidence
No of cases per 100 thousand women at a 95% confidence Interval
Married Yes 880 4211,0 3 71,2 (14,6 — 207,9)
No 1797 8895,5 1 11,2 (0,28 — 62,3)
Unmarried Yes 349 1466,5 3 204,6 (42,1 — 597,4)
No 790 3255,0 6 184,3 (67,6 — 401,7)
Total 3816 17 828 13 72,9 (38,7 — 123,9)
Table 6
BC incidence in nulliparous women respective of body weight
Weight, kg No of women under surveillance No of surveillance man-years Incidence
No of cases per 100 thousand women at a 95% confidence interval
49 57 248 — —
50 — 59 361 1556 2 128,5 (15,5 — 463,8)
60 — 69 896 4017 2 49,8 (6,0 — 179,7)
70 — 79 751 3423 3 87,6 (18,0 — 255,7)
80 — 89 540 2503 1 39,9 (0,9 — 222,2)
90 — 99 183 845 — —
100 78 358 — —
Total 2866 12 950 8 61,7(26,5 — 121,5)
relative risk of BC occurrence in nulliparous women depending upon individual factors (table 7).
Our study discovered the relative risk (RR) of BC occurrence in nulliparous women to be 28% higher than that among all the women under surveillance (RR=1.28), but the difference was not statistically significant.
Abortions and family status were determinant factors in BC incidence among childless women.
Abortions lead to a 33% increase in the risk among chidless women (RR is 11.44), however this difference is not statistically significant. Family status exerts statistically significant influence on BC incidence. Childless unmarried women have a 2.33-fold higher risk of BC occurrence as compared to all childless women.
Table 7
Relative risk of BC incidence in nulliparous women in respect of individual factors
Woman group and factors Relative risk
All nulliparous women 1.0
Including women: 1,44 (0,1 - 3,4)
having abortions 2,33 (1,0 — 5,4)
unmarried 2,53 (1,6 — 4,8)
having no abortions 2,23 (1,7 — 3,1)
married, having no abortions 0,16 (0,01 — 0,17)
Unmarried women with a history of abortions have a higher risk of BC incidence among nulliparous women. The risk is 2.5-fold as high as among the whole cohort of childless women.
We suppose that the absence of pregnancies also has effect on BC risk. This consideration is confirmed by the fact that nulliparous women without abortions have a 2.23-fold higher relative risk of BC than all nulliparous women.
The relative BC risk among married nulliparous women without abortions is 0.16, i.e. 5-fold as low as in all nulliparous women. However, the difference calculated with respect to 95% confidence interval was not statistically significant.
Thus, BC incidence in nulliparous women may vary considerably because it is determined by composition of the group under study as regards family status and abortions, rather than by the factor of no deliveries.
