http://www.cancer.gov/cancertopics/factsheet/Risk/oral-contraceptives
Scroll down to Item #2, second paragraph.
THAT is NOT a “control group”!
A control group would be following a group of 200 women who had never taken BCPs and counting the incidence of breast cancer in the group.
This was a count of women who had breast cancer and then asking their history.
This has the effect of beginning with a polluted sample, not a control group!