Morgan,
This is a new paper (pasted below) but it only found a never vs ever (rather 
than a dose dependent relationship- given it's a US study this is not 
surprising). It could however be used as evidence that bf is particularly 
important for women with a history of breast cancer. The paper that I most 
frequently use looking at breast cancer is old but it's pretty much the only 
one that looked at decent durations of breastfeeding. It compared women who 
had breastfed each child for up to 6 months vs 2+ years. Women who had 3 
children and had bf each for 2+ years had half the risk of breast cancer as 
women who had bf each child for up to 6 months.
Hope this helps
Karleen Gribble
Australia

Stuebe, A. M., W. C. Willett, et al. (2009). "Lactation and Incidence of 
Premenopausal Breast Cancer: A Longitudinal Study." Arch Intern Med 169(15): 
1364-1371.
	Background Findings from observational studies suggest an inverse 
association between lactation and premenopausal breast cancer risk, but 
results are inconsistent, and data from large prospective cohort studies are 
lacking. Methods We used information from 60 075 parous women participating 
in the prospective cohort study of the Nurses' Health Study II from 1997 to 
2005. Our primary outcome was incident premenopausal breast cancer. Results 
We ascertained 608 incident cases of premenopausal breast cancer during 357 
556 person-years of follow-up. Women who had ever breastfed had a 
covariate-adjusted hazard ratio (HR) of 0.75 (95% confidence interval [CI], 
0.56-1.00) for premenopausal breast cancer compared with women who had never 
breastfed. No linear trend was found with duration of total lactation (P = 
.95), exclusive lactation (P = .74), or lactation amenorrhea (P = .88). The 
association between lactation and premenopausal breast cancer was modified 
by family history of breast cancer (P value for interaction = .03). Among 
women with a first-degree relative with breast cancer, those who had ever 
breastfed had a covariate-adjusted HR of 0.41 (95% CI, 0.22-0.75) for 
premenopausal breast cancer compared with women who had never breastfed, 
whereas no association was observed among women without a family history of 
breast cancer. Conclusion In this large, prospective cohort study of parous 
premenopausal women, having ever breastfed was inversely associated with 
incidence of breast cancer among women with a family history of breast 
cancer.


Zheng, T., L. Duan, et al. (2000). "Lactation reduces breast cancer risk in 
Shandong Province, China." American Journal of Epidemiology. 152(12): 
1129-1135.
	Results from studies of western populations investigating lactation and 
breast cancer risk have been inconsistent. To examine this issue, the 
authors conducted a hospital-based case-control study in Shandong Province, 
China, in 1997-1999. A total of 404 cases and an equal number of controls 
were included. Detailed information regarding lactation, menstruation, and 
reproduction was collected through in-person interview. The authors found a 
significant inverse association between duration of lactation and breast 
cancer risk. For women who breastfed for more than 24 months per child, the 
odds ratio was 0.46 (95% confidence interval (CI): 0.27, 0.78) when compared 
with those who breastfed for 1-6 months per child. A significantly reduced 
risk of breast cancer was also found for those whose lifetime duration of 
lactation totaled 73-108 months (odds ratio = 0.47, 95% CI: 0.23, 0.95) and 
for those who breastfed for > or =109 months (odds ratio = 0.24, 95% CI: 
0.11, 0.53). The test for trend was statistically significant for both mean 
duration of lactation per child (p = 0.02) and lifetime duration of 
lactation (p = 0.00). Further stratification by menopausal status resulted 
in the same conclusion. These data suggest that prolonged lactation reduces 
breast cancer risk.




--------------------------------------------------
From: "Morgan Gallagher" <[log in to unmask]>
Sent: Wednesday, September 02, 2009 7:11 AM
To: <[log in to unmask]>
Subject: Reducing breast cancer risks - cites

> I'm currently preparing an advocacy statement for a 20 month old, female
> child.
>
> The father is arguing that breastfeeding is a control mechanism by the
> mother.
>
> The maternal grandmother died of breast cancer at a young age.  The
> mother is aware that the longer she can maintain breastfeeding, the more
> the risks of both her, and her daughter, developing breast cancer, are
> mitigated.
>
> I'm therefore looking for cites, on breast cancer risk and breastfeeding
> - much of what I've found on established sites, such as Kellymom etc,
> are quite old.  I'd be really happy if one could be found with a nice
> pithy line to quote, about the duration of breastfeeding being an
> important factor.  :-)
>
> Many thanks...
>
> Morgan Gallagher
>
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