Abortion/cancer

About
It is often claimed that abortion leads to a higher risk of cancer. All reputable sources seem to be saying that this is nonsense and that there are no known health risks to abortion when compared to natural birth, but it is difficult to find links to the specific studies regarding this matter.

From the papers I have been able to find, there appears to be mixed evidence that there may be a link, but it is a weak effect.

Scientific Publications

 * 2013-08-09 Induced abortion and breast cancer Wiley PubMed (Patrick Carroll): no abstract; article behind paywall
 * 2013-07-19 Abortion-breast cancer study not valid for assessing overall association. criticizes a study by Bra&uuml;ner et al. which found no link. Can't seem to find the study to which it refers.
 * 2004-03-27 Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83 000 women with breast cancer from 16 countries (Collaborative Group on Hormonal Factors in Breast Cancer) "The overall relative risk of breast cancer, comparing women with a prospective record of having had one or more pregnancies that ended as a spontaneous abortion versus women with no such record, was 0·98 (95% CI 0·92—1·04, p=0·5). The corresponding relative risk for induced abortion was 0·93 (0·89—0·96, p=0·0002)." It's not clear whether they compare with women who had no abortions at all.
 * 2004-06-05 Abortion and breast cancer: letter from David C. Reardon praising the above study
 * 2002-05 On the relation between induced abortion and breast cancer. (Joel Brind, Vernon M Chinchilli) "Davidson misrepresents our study as a “simple numerical count of papers” and he uses three papers to our one, to argue that the evidence of a causal link is not conclusive. On this evidence he advocates against telling women considering abortion, that there is an increased risk of breast cancer."
 * 2001-04-28 Cancer paper retracted "the Journal of Clinical Oncology retracted a paper on high-dose chemotherapy for breast cancer on April 26 [...] The South African study was by Werner R Bezwoda and colleagues: “High-dose chemotherapy with hematopoietic rescue as primary treatment for metastatic breast cancer" (J Clin Oncol 1995; 13: 2483—89).
 * 1994-11-02 Risk of breast cancer among young women: relationship to induced abortion. (Daling JR, Malone KE, Voigt LF, White E, Weiss NS.) "Our data support the hypothesis that an induced abortion can adversely influence a woman's subsequent risk of breast cancer. However, the results across all epidemiologic studies of this premise are inconsistent--both overall and within specific subgroups. The risk of breast cancer should be reexamined in future studies of women who have had legal abortion available to them throughout the majority of their reproductive years, with particular attention to the potential influence of induced abortion early in life."