Does breast fat transfer increase the risk of breast cancer?

Thanks for your excellent questions. There is no evidence to date that fat transfer increases the risk of breast cancer. However, it can increase the risk of causing changes on mammograms which may lead to unnecessary investigation, so it is important that you let your breast team know if you are having breast cancer surveillance.
If fat is injected directly into a major vessel, then you can get a 'fat embolus' and this can be life threatening. This has been reported following fat injection for buttock augmentation, but is not associated with fat transfer to the breasts.
It would be possible to increase size from A-C cup if you have enough donor fat available and are willing to undergo multiple procedures in order to achieve your desired volume. If you have had your implants removed, another option may be to combine an uplift procedure with some fat transfer.

In general, 200 cc per breast is typically the upper limit of fat injection recommended by most plastic surgeons.  It is not that more cannot be injected; but on average, this has been determined to be the most that can be expected to live during one transfer.  The fat must be injected through multiple planes in small amounts to the tissue through one tiny incision under each breast.  If you want more than a one cup size increase, this may require multiple treatments to reach the size you desire.
Fat transfer to the breast could improve the fullness of the breast, particularly at the top of the breast.   About 50% of the fat obtains permanence.  Calcification can occur after any fat transfer procedure.  I am not sure that the data has been collected on rate of calcification, and then the issue becomes whether that is clinically significant. The calcifications can be delineated from those for malignancy.
Kenneth Hughes, MD, Board Certified Plastic Surgeon

There was a concern previously that fat grafting may result in calcification that could be confused with breast cancer on mammography. This has subsequently been shown to be a minimal risk. There is no concern that the fat grafting actually causes cancer however. The fat survives as a graft in the new location and it is a permanent transfer of the fat and should survive for your lifetime. It behaves like fat anywhere else however and if you put on weight it will get larger, and if you lose weight it will get smaller. The "take" of the graft varies somewhat, but with careful technique 70% or more of the graft should survive. The volume change depends on the space available for fat injection. If you have laxity of the skin following the implant removal a higher volume may be possible. In order to get a change from A to C cup size it may require more than one session of fat grafting. Accidental intravenous injection of fat is a higher risk for buttock augmentation. Careful use of blunt cannulae reduces this risk. I don't see any problem with moderate use of alcohol after fat grafting.