The pushback against soaring cancer drug prices is gaining steam. 

A leading doctors group on Monday proposed a formula to help patients decide if a medicine is worth it - what it will cost them and how much good it is likely to do.

The move by the American Society of Clinical Oncology is the third recent effort to focus on value in cancer care. Two weeks ago, the European Society for Medical Oncology proposed a similar guide. Last week, Memorial Sloan Kettering Cancer Center in New York posted an online tool suggesting a drug's fair price, based on benefits and side effects.

"We have a broken system" with drug prices rising more than the degree of benefit, said Dr. Peter Bach, director of the Center for Health Policy and Outcomes at Sloan Kettering. "We hope consumers increasingly think about value."

New cancer drugs typically cost more than $10,000 a month, and patients are paying a greater share through higher copays and deductibles.

"We have extraordinarily expensive technology that we have developed but a lot of it doesn't seem to move the needle that much" in terms of survival, Michael Porter, a Harvard Business School economist, told an audience at the U.S. oncology group's annual conference last month.

Patients often are not fully aware of costs, which include not just the drug but also whether a patient needs to be hospitalized to get it, or to take other drugs to manage side effects, he said.

The formula is something doctors can work through with patients to get a bottom line on the survival benefit, side effects and costs of a new treatment or combo versus older ones.

So far, it's just a prototype for four situations - lung or prostate cancer that has spread, advanced multiple myeloma and a common type of breast cancer. The group will take comments from the public until Aug. 21 and plans similar efforts for other types of cancer.

In the formula, treatments are given scores for how much they improve survival or the time until cancer worsens. For advanced cancers, bonus points are given for drugs that greatly relieve symptoms or give patients a break from treatment. Side effects also are scored, and the points are combined to get a "net health benefit."

The bottom line will mean different things to different patients, said the head of the 24-expert panel that developed the tool, Dr. Lowell Schnipper, cancer center chief at Boston's Beth Israel Deaconess Medical Center. For example, a drug may boost survival more than another one, but cause hand numbness that would greatly bother a violinist, he said.

"There is that kind of tradeoff in much of what we offer patients," so each person needs to judge value for himself, he said.

The final step is to compare costs. The tool gives drug prices provided by insurer UnitedHealthCare as a guide, but they vary greatly among hospitals, and copays depend on each person's insurance plan.

The formula was published online Monday by the Journal of Clinical Oncology.