Eli Lilly & Co. and Merck KGaA’s Erbitux failed to help colon cancer patients in a study, which may leave doctors less likely to combine the drug with a certain type of chemotherapy. However, the drug was found to delay the spread of breast cancer by about two months in a study of women with a certain type of aggressive tumor.

Erbitux didn’t slow or delay the progression of colon-cancer tumors and didn’t prolong patients’ lives, according to a study released Sunday at the European Society for Medical Oncology conference in Milan. Patients with a normal version of a gene called KRAS didn’t respond better than those with a mutation.

The results add to a growing body of evidence that Erbitux, known chemically as cetuximab, might not work in certain chemotherapy combinations, said Kjell Magne Tveit, an oncologist at Oslo University Hospital and a researcher on the study. The drug didn’t keep colon cancer at bay in a U.K. trial last year. That trial combined Erbitux with oxaliplatin, the same chemotherapy as in Sunday's study.

“The results from our study and the [U.K.] study together really question whether cetuximab has a clinically significant effect in first line,” Tveit said in a statement.

Erbitux is approved for advanced colon cancer as well as head and neck tumors. Last year, its prescribing information was changed to say the drug won’t help the roughly 40 percent of people whose tumors have the KRAS gene mutation.

“The findings are not consistent with current scientific understanding” of the way Erbitux works, and contradict previous trials, Merck spokeswoman Phyllis Carter said by telephone.

The German drugmaker’s own study, combining Erbitux with a different type of chemotherapy called FOLFIRI, found Erbitux helped normal KRAS patients live an average of 3.5 months longer than those given chemotherapy alone. A second study using a chemotherapy mixture called FOLFOX, which combines oxaliplatin in a different way, also found that Erbitux helped patients, Carter said.

Dubbed NORDIC VII, the trial for which results were released Sunday followed 566 patients from Sweden, Denmark, Norway, Finland and Iceland. Like last year’s U.K. study, the trial was conducted independently from Merck.

However, adding Erbitux to chemotherapy lengthened the time before patients’ cancer progressed from a median 1.5 months to 3.7 months, according to a mid-stage study released Monday at the same European Society for Medical Oncology conference. Twenty percent of Erbitux patients saw their cancer shrink or disappear, versus 10 percent of those on chemotherapy alone.

While Erbitux didn’t provide as large a benefit as researchers had targeted, the results from the 173-patient study show that the drug has “a role in treating breast cancer,” lead researcher Jose Baselga, associate director of the Massachusetts General Hospital Cancer Center in Boston, said in a conference call with reporters.

“The study in my mind is vastly positive,” Baselga said. The results may be grounds for the bigger final-stage studies that would be needed to win regulatory approval for the use of Erbitux against breast cancer, he said.

Monday’s study used a different kind of chemotherapy than that used in the colon-cancer trials.

Merck will make a final decision about whether to pursue more trials of Erbitux in breast cancer after final results from Monday’s study are available, spokeswoman Phyllis Carter said by e-mail.

Lilly, based in Indianapolis, and New York-based Bristol- Myers Squibb Co. market Erbitux in the U.S., while Merck, based in Darmstadt and unrelated to the U.S. drugmaker Merck & Co., sells it elsewhere.