Celgene’s Abraxane and Bristol- Myers Squibb’s Ixempra breast-cancer drugs worked no better at delaying tumor growth than a less-expensive chemotherapy that’s been the backbone of treatment for 20 years.

Newly treated patients taking paclitaxel, a generic drug, lived a month longer than those given Abraxane, a modified form of the same medicine, and three months longer than those taking Ixempra, according to data reported Monday at the American Society of Clinical Oncology meeting in Chicago.

Abraxane and Ixempra cost between $4,000 and $5,000 a dose, according to their manufacturers. The price of paclitaxel varies though it is significantly less than the newer treatments, said Hope Rugo, a breast cancer specialist at the University of California, San Francisco and a study researcher. The price difference may prompt some doctors to reconsider Abraxane as an initial treatment in certain patients, said Shanu Modi, an oncologist at Memorial Sloan-Kettering Cancer Center in New York.

“As a global issue, it is difficult to justify using a more expensive drug if an equally active drug is available that costs less,” Modi said in an interview. “This is not going to help Abraxane.”

Abraxane is one of top-selling products sold by Summit, N.J.-based Celgene, with $386 million in sales last year, according to data compiled by Bloomberg. Ixempra generated $100 million in revenue for Bristol-Myers, based on New York.

Celgene has said it expects Abraxane sales of as much as $1.2 billion in 2015 as it expands its use in other tumors. The drugmaker paid $2.9 billion to acquire Abraxane’s maker, Abraxis BioScience, in 2010. Abraxane’s “nab” technology combines paclitaxel with the protein albumin, enabling the drug to be given at a higher dose and breach blood vessel walls more effectively, according to the company.

Greg Geissman, a Celgene spokesman, said the company couldn’t comment on the study because it hadn’t reviewed the full data yet. Bristol-Myers spokeswoman Sarah Koenig said the results from the study don’t impact the indications for Ixempra.

While neither Abraxane nor Ixempra are approved for previously untreated patients, doctors said they use them in certain patients as an initial treatment.

Kimberly Blackwell, a breast cancer specialist at Duke University Medical Center, said she will still consider giving Abraxane to some of her patients because it is easier to administer and doesn’t have the risk of allergic reaction that paclitaxel carries.

To avoid an allergic reaction to paclitaxel, patients have to take steroids, which carry their own risks and add an hour to patients’ weekly treatments. Abraxane doesn’t usually cause an allergic reaction so steroids aren’t needed.

“If I were a patient, I would prefer not to have to take the pre-medication associated with paclitaxel,” said Blackburn. “An extra hour each week to take the pre-meds adds up.”

Abraxane and paclitaxel are both from the same class of medicines called taxanes, while Ixempra is from a group called epothilones, which work similarly and given to patients whose disease is taxane resistant.

Patients given Abraxane with Roche’s Avastin had 9.2 months before their tumors progressed compared to 10.6 months for those on paclitaxel and Avastin.

Patients in a third group who took Bristol’s Ixempra with Avastin had 7.6 months without disease progression. The study followed 799 patients given Avastin with either paclitaxel, Abraxane or Ixempra. Serious side effects were lowest in patients taking Ixempra and highest in the Abraxane group.

— With reporting by Robert Langreth in Chicago.