A doctors group is proposing a formula to help cancer patients decide if a drug 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 latest of several recent efforts to focus on value in cancer care.

New drugs often cost more than $10,000 a month and patients are paying a greater share through higher copays and deductibles. The group's tool is a formula doctors can work through with patients to get a bottom line on the survival benefit, side effects and cost of a new treatment or combination versus older ones.

The proposal was published online Monday by the Journal of Clinical Oncology. Patients can comment until Aug. 21.