Ignoring the cost of care, though, is no longer tenable. Soaring spending has presented the medical community with a new obligation. When choosing treatments for a patient, we have to consider the financial strains they may cause alongside the benefits they might deliver.

This is particularly the case with cancer, where the cost of drugs, and of care over all, has risen precipitously. The typical new cancer drug coming on the market a decade ago cost about $4,500 per month (in 2012 dollars); since 2010 the median price has been around $10,000. Two of the new cancer drugs cost more than $35,000 each per month of treatment.

The burden of this cost is borne, increasingly, by patients themselves — and the effects can be devastating. In 2006, one-quarter of cancer patients reported that they had used up all or most of their savings paying for care; a study last year reported that 2 percent of cancer patients were driven into bankruptcy by their illness and its treatment. One in 10 cancer patients now reports spending more than $18,000 out of pocket on care.

Which brings us back to our decision on Zaltrap. In patients with advancing, metastatic colorectal cancer, the new drug, approved by the F.D.A. in August and jointly marketed by Sanofi and Regeneron, offers the same survival benefit as Genentech’s Avastin, which works through a similar molecular mechanism. When compared with the standard chemotherapy regimen alone, adding either medicine has been shown to prolong patient lives by a median of 1.4 months. Major clinical practice guidelines, like those from the National Comprehensive Cancer Network, agree that Zaltrap is no better than Avastin in this setting. (Full disclosure: Two of us, Dr. Bach and Dr. Saltz, have been paid consulting fees by Genentech.)

But Avastin costs roughly $5,000 a month: very expensive in its own right, yet less than half of Zaltrap’s price tag. And while the side effects in both drugs are roughly equal, doses of Avastin generally take less time to administer than those of Zaltrap, which makes Avastin more convenient for patients.