Tamoxifen, which is also available as a sugar free liquid called Saltamox, often comes with hormonal side effects and blood clotting.
Now a study by Northwestern University in Chicago has now shown that using it in gel form is as effective in treating the cancer, while limiting these side effects.
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The research has been welcomed by Breakthrough Breast Cancer Scotland, which said it was promising.
Director James Jopling said: "We know that tamoxifen is a highly effective drug for both treating breast cancer and also, as recently recommended, for preventative use in those at high risk of breast cancer because of their family history.
"While tamoxifen use for breast cancer prevention has been described as a game changer, the side effects associated with the drug do put some women off taking it, so this research is promising.
"The study showed women who applied the gel had similar levels of tamoxifen in the breast tissue to those taking the pill version, which is the normal form in which the drug is taken, and lower levels of the drug in their blood - which could lead to fewer side effects."
He added: "Although these findings are very interesting, the research was conducted over a short time period on a small group of women who already had an early form of breast cancer.
"Results have not yet proved that tamoxifen gel can prevent breast cancer or that there will be fewer side effects compared to the pill form.
"Once more research has been carried out and we begin to see further results, this could be an exciting development for breast cancer prevention in those at higher risk in the future."
The researchers randomly assigned 26 women with breast cancer either the gel or the oral form of the drug and monitored the results for 10 weeks.
They found that the results in treating the disease were comparable, but the level of the drug in the blood was lower, resulting in fewer side effects.
Professor Seema Khan, who led the research, said: "In this study, we have shown that the gel application to the skin resulted in high drug levels in the breast but low drug levels in the circulation. This would maintain the effectiveness of the drug, but minimize the side effects.
"Oral tamoxifen is used by some women at high risk for breast cancer to prevent the development of the disease, and our data suggests that gel application of tamoxifen could replace this approach, thus encouraging more women to adhere to preventive therapy."