The referenced 1994 study done by Daling and Rosenberg involved 845 women in Washington state who were diagnosed with breast cancer. Although the study did conclude a positive correlation between abortion and breast cancer, its authors, themselves, concluded that the study's "limitations argue against a firm conclusion at this time" and called for further research.
More recent research in Denmark and Sweden studied 1.5 million and 45,000 women respectively and concluded no connection. Although several smaller U.S.-based studies have concluded the same thing, experts put considerable weight on the Scandinavian studies because of the large number of participants and the fact that their health care system allows researchers to gain complete access to health records, avoiding unintentional errors that occur when participants are asked to recall events from the past.
A New York Times article dated March 7, stated that the National Cancer Institute was changing their website from the link being "inconclusive" to "no association between abortion and breast cancer risk." This change was made when two panels of experts convened to examine four new studies and re-evaluate older studies including Daling's and Rosenberg's.
Kelly Crowley, Roundup