1984; Ellery et al., 1986; Meirik et al., 1986; La Vecchia et al., 1986; Paul et al., 1986; Lee et al., 1987; Ravnihar et al., 1988; Schlesselman et al., 1988). It is possible, however, that these studies were conducted too early to see such an effect.

Use of Oral Contraceptives in High-Risk Subgroups

Although many investigators adjust for high-risk factors (e.g., family history of breast cancer, history of benign breast disease) in their analyses, only a subset have examined oral contraceptive use within each of these strata. Furthermore, of the few studies that have examined oral contraceptive use in each strata, the majority have limited their definition of use to “ever/never” and their definition of the high-risk subgroups to fairly crude delineations (i.e., “ever/never” had sister with breast cancer). These approaches are unfortunate because they may well miss important modifying relationships that cannot be detected at such a crude level.

With regard to family history of breast cancer, the bulk of the studies have detected no substantial differences in the risk related to oral contraceptive use for women with and without this factor (Miller et al., 1989; Murray et al., 1989; Romieu et al., 1989). Brinton and colleagues (1982) found no differences in women with and without a mother with breast cancer but did see differences in women with and without a sister with breast cancer.

Elevated risks have been observed for oral contraceptive use among women with a history of benign breast disease (Fasal and Paffenbarger, 1975; Lees et al., 1978; Brinton et al., 1982; Janerich et al., 1983); but more work is needed to evaluate specific histologic types of benign breast disease in terms of both breast cancer risk and relationship to use of the pill. Some past analyses failed to distinguish between oral contraceptive use before and after the diagnosis of benign breast disease (Stadel and Schlesselman, 1986). In addition, not much has been done to examine histologic subgroups of breast cancer for the possibility of differential relationships with oral contraceptive exposure.

Steroidal Potency of Various Formulations

The hormonal contents of oral contraceptives have been examined by a number of classification schemes related to potency, brand, and type of estrogen (Brinton et al., 1982; Harris et al., 1982; Pike et al., 1983; Vessey et al., 1983; Stadel et al., 1985; Ellery et al., 1986; CASH, 1986; Miller et al., 1986; McPherson et al., 1987; Schlesselman et al.,



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