Overall risk of developing cancer over a lifetime is similar among women who have used COCs and women who have not used COCs. COC users may have small increases in risk of some types of cancer, but they also have long-term reductions in other types of cancer.

Ovarian and endometrial cancer

• Use of COCs helps protect users from 2 important kinds of cancer—cancer of the ovaries and cancer of the lining of the uterus (endometrial cancer).
• This protection continues for 15 years or more after stopping use of COCs.

Breast cancer

• Research findings about COCs and breast cancer are difficult to interpret:
  • Studies find that women who used COCs more than 10 years ago face the same risk of breast cancer as similar women who have never used COCs. In contrast, some studies find that current users of COCs and women who have used COCs within the past 10 years are slightly more likely to be diagnosed with breast cancer. On balance, there may be little difference in lifetime risk. It is unclear whether these findings are explained by earlier detection of existing breast cancers among COC users or by a biologic effect of COCs on breast cancer.
  • Previous use of COCs does not increase the risk of breast cancer later in life, when breast cancer is more common.
  • When a current or former COC user is diagnosed with breast cancer, the cancers generally are less advanced than cancers diagnosed in other women.
  • COC use does not increase risk of breast cancer for women whose relatives have had breast cancer.

Cervical cancer

• Cervical cancer is caused by certain types of human papillomavirus (HPV). HPV is a common sexually transmitted infection that usually clears on its own without treatment, but sometimes it persists and sometimes leads to cervical cancer. A vaccine can help to prevent cervical cancer. (See the section on Cervical Cancer in Chapter 22.) If cervical screening is available, providers can advise all women to be screened every 3 years (or as national guidelines recommend).
• Use of COCs for 5 years or more appears to increase slightly the risk of cervical cancer. After a woman stops using COCs, this risk decreases. By 10 years after stopping COCs, a former COC user has the same risk of cervical cancer as a woman who has never used COCs. The number of cervical cancers associated with COC use is small.

Other cancers

• Use of COCs may decrease the risk of colorectal cancer.
• There is no clear evidence that COC use either decreases or increases the risk of any other type of cancer.