New targeted therapies — drugs that attack only cancer cells, leaving most normal cells unharmed — are needed to continue the significant progress made in recent years against breast cancer, said a leading British cancer expert in The Lancet (Vol. 360, No. 9335: 790-792).

"The development of targeted therapy for specific treatments is an increasingly important goal," said Ian E. Smith, MD, medical director of the Institute of Cancer Research in London, England.

That's because such therapies are likely to be more effective and have fewer side effects than conventional treatments such as chemotherapy. Yet only one such drug for breast cancer is available now, and it works only on breast cancers with a particular target not all breast cancers have, Smith noted.

Only one new chemotherapy drug approved in the last 10 years — docetaxel (Taxotere) — seems to be better at shrinking tumors in advanced breast cancer than the anthracycline drugs long considered the best standard therapy, but it hasn't helped those patients live longer, Smith said.

Docetaxel may help early-stage breast cancer patients live longer when combined with other drugs. But more patients have troublesome side effects, a common pattern with combinations of the new drugs, that makes many doctors hesitant to use them, said Smith.

And the number of possible new combinations is very large, requiring many more studies to learn how to use them best, Smith commented.

New hormone therapy drugs called aromatase inhibitors are proving much more effective in many situations than the older drug tamoxifen, said Smith.

In women with advanced stage breast cancer, two of these new drugs, anastrozole and letrozole, work in more patients and delay cancer growth longer compared to tamoxifen, Smith said.

A recent study indicated that anastrozole may be better than tamoxifen after surgery for early stage cancer, reducing the chance that the cancer will return.

Letrozole may also prove to be better than tamoxifen at shrinking tumors in women with early stage disease even before surgery. This may allow some women to have a lumpectomy instead of having the entire breast removed, said Smith.

But more study is needed to determine the drugs' long-term effects. So for now, tamoxifen remains the hormone drug of choice for women past menopause in most situations, said Smith.

And the drugs shouldn't be used by women who have not gone through menopause, Smith noted.

In a study reported recently in the Journal of Clinical Oncology, researchers said a new drug called fulvestrant is being used in women who have hormone-sensitive tumors when tamoxifen is no longer effective. The authors said that fulvestrant was at least as effective as anastrozole in women who had previously taken tamoxifen.

Because breast cancer often spreads to the bones, drugs called bisphosphonates, such as pamidronate and clodronate, are useful in helping to protect them.

A recent study suggested that clodronate may actually reduce the spread of breast cancer to the bone in the first place, helping patients live longer, Smith said. Clodronate is not available in the US at this time.

Other such drugs need more study, but bisphosphonates can be especially helpful when hormone therapies are used that could thin bones, said Smith.

The one targeted therapy approved for breast cancer, trastuzumab (Herceptin), when used with chemotherapy, shrinks tumors in more patients, keeps cancer growth stopped longer, and lengthens patients' lives, compared to chemotherapy alone, Smith said.

It is now being studied alone as a first therapy for advanced breast cancer. In one study, Herceptin shrank tumors for more than a year, with few side effects, said Smith.

But like all targeted therapies, Herceptin works only against cancers whose cells have the abnormality the drug targets. Only about 25% of all breast cancers have this abnormality.

New targeted therapies that can attack targets present on more breast cancer cells are needed, said Smith.

"More effective drugs are very badly needed for breast cancer, especially for advanced breast cancer," said Otis Brawley, MD, associate director of the Winship Cancer Institute of Emory University in Atlanta.

More women are surviving breast cancer than ever before, but mainly because more cancers are being found early with mammography, and because treatments for early stage cancers have improved, said Brawley.

The good news is that targeted therapies are being developed at a faster pace than ever before, noted Brawley.

While most recently approved targeted therapies are for leukemias and lymphomas, several different kinds of drugs targeted against growth-promoting substances on breast cancer cells are being developed and are looking very promising, Brawley said.

"The progress we have made against early stage breast cancer is wonderful, but we must continue to do everything possible to bring more effective drugs to patients, because they are badly needed, and they cannot come too soon," said Brawley.