For women who are recovering from breast cancer and require anti-estrogen drugs to prevent recurrence, a new topical drug applied to the breasts may be effective. A gel version of the widely prescribed drug Tamoxifen may bring more benefit and fewer serious side effects than the oral form.

Tamoxifen is used in men and women to treat breast cancer that has spread to other parts of the body and to treat early breast cancer in women who have already had surgery, radiation, and/or chemotherapy. It can help reduce the risk of a woman's developing a more serious type of breast cancer if she has had ductal carcinoma in situ (DCIS).

DCIS is a type of breast cancer that does not spread outside of the milk duct where it forms. Women with DCIS are often given Tamoxifen after they have been treated with surgery and radiation. It is also sometimes used to reduce the risk of breast cancer in women who are at high risk for the disease.

Despite its value as a cancer treatment, the drug has two very serious side effects. It can cause blood clots and uterine cancer.

Tamoxifen is an antiestrogen. It blocks the activity of the female hormone estrogen in the breast. This may prevent the growth of some breast tumors that need estrogen to grow.

The subjects in the new study were a group of women, aged 45 to 86, who’d battled DCIS. Half of the women received the regular daily oral form of Tamoxifen and half received the gel version of the drug, which they applied to their breasts daily.

After six to 10 weeks of the respective routines, the results were promising: A marker for breast cancer cell growth was reduced by about the same amount in both groups. And even more exciting, the blood level of the medication was significantly lower among the women using the gel as compared to those taking the oral medication.

This is important because despite its value as a cancer treatment and preventive, the drug has two very serious side effects. It can cause blood clots and uterine cancer.

The last thing doctors want an anti-cancer medication to do is to raise other serious health risks for the person taking it. But to be effective for breast cancer prevention and DCIS therapy, certain levels of drug concentrations are required in the breast.

These side effects should be reduced with the gel, researchers believe, because the gel keeps the drug concentrated where it is needed, in the breast, rather than the blood stream or other parts of the body where it can cause problems.

“There was very little drug in the bloodstream which should avoid potential blood clots as well as an elevated risk for uterine cancer…[H]igh circulating drug levels only cause collateral damage,” study author Seema Khan said in a news release.

The gel form may also be more effective for certain women, since about a third of women lack the liver enzyme needed to break down the oral form of Tamoxifen, which means it’s ineffective in these cases.

The gel form of Tamoxifen could one day replace the oral form, if it lives up to its promise. More research will be needed, but from the early results researchers are hopeful.

The study was carried out by a team at Northwestern University and published in the journal, Clinical Cancer Research.