According to new studies, drugs used widely to treat anemia in cancer patients may actually speed progression of the cancer in certain individuals, "The Washington Post" reported June 2.

Recent controversy over erythropoiesis-stimulating agents (ESAs) such as Procrit, Epogen and Aranesp

In March, an FDA advisory panel voted to recommend continued use of the drugs for patients on chemotherapy, unless the patient is likely to be cured. They also voted to recommend against the drugs' use in patients with breast or head and neck cancer.

The drugs' manufacturers added a "black box" warning to the medications last November. Eight clinical trials now suggest these medications actually speed the growth of tumors and shorten the lives of cancer victims, the Post reported.

The results of the current study were based on analyses of tumor samples from 101 patients diagnosed with head and neck cancer who had participated in a previous phase III trial of erythropoietin. Scientists measured levels of erythropoietin receptor (EpoR) messenger RNA (mRNA). High levels of EpoR mRNA in patients who had undergone radiation but not surgery tended to signal a worse prognosis. There was a similar effect with Janus Kinase 2 (Jak2), the main intermediary of EpoR signaling.

A second study found the multiple drugs elderly cancer patients may already be taking could interact significantly with chemotherapy.

In particular, patients taking drugs that interfered with protein binding, such as Norvasc for high blood pressure, Prilosec for heartburn and the pain reliever Celebrex, were more likely to experience hematologic side effects such as low white blood cell counts.

Patients taking drugs that act on a group of enzymes known as cytochrome p450 were more likely to experience effects such as fatigue or diarrhea. Examples of these drugs include the heart medications such as Pacerone and Cordarone.