Pfizer drug effective in rare children's cancers (Reuters) - A Pfizer Inc lung cancer drug appears to be a highly effective treatment for children with a rare but aggressive type of lymphoma and other cancers, according to data from an early stage study released on Wednesday. The drug, crizotinib, was able to stall tumor growth and in some cases eradicate all signs of particularly aggressive cancers with minimal side effects, researchers said. The study highlights a new understanding of how some cancers operate, one that is based on the patient's genetic profile rather than the organ in which the tumor originates. The hope is that by identifying more instances of a genetic connection, doctors will be better able to target a drug for treatment. Crizotinib, sold under the brand name Xalkori, is approved to treat non-small cell lung cancer in patients with a specific gene mutation known as ALK. But some patients with other types of cancer have also been found to have abnormal ALK, including those suffering from anaplastic large cell lymphoma (ALCL), a cancer of the lymph cells, researchers said. In the study conducted by the Children's Oncology Group, seven of eight children with ALCL had a complete response to the drug, meaning no cancer could be detected with imaging scans. "It's remarkable that this targeted oral medication provided such a substantial benefit in these children with highly aggressive cancers, most of whom had already undergone every available therapy," Dr Yael Mosse, the study's lead researcher from the Children's Hospital of Philadelphia, said in a statement. Dr Michael Link, president of the American Society of Clinical Oncology (ASCO) and a pediatric oncologist, characterized the response rates as "pretty phenomenal." He was not involved in the research. "The durability of the response is pretty amazing," he said. The study included 70 children whose various cancers had progressed after being treated with standard therapies. Determining the safety of crizotinib in children was the primary goal of the Phase I study that tested the drug at several doses. Of the children in the study who could be fully evaluated for drug toxicity, toxic side effects were deemed to be minimal, even though many of the crizotinib doses tested were relatively high, researchers said. The drug was exceedingly well-tolerated. Most toxicities were extremely low grade and did not impact quality of life," Mosse told reporters on a conference call. The studied doses ranged from 100 milligrams to 365 mg. Based on the study findings, researchers determined that the recommended dose for children in future studies will be 280 mg, roughly twice the adult-recommended dose. The data will be presented at next month's ASCO meeting in Chicago, but was released on Wednesday along with summaries of hundreds of other studies that will be featured at the year's most important cancer meeting. The study also tested crizotinib - a pill taken twice a day for 28-day cycles - in 27 children with neuroblastoma, a difficult-to-treat cancer of the nervous system, and in seven children with a rare form of sarcoma. The trial, however, was not restricted to patients with known ALK abnormalities and was open to those with certain cancers that had relapsed or did not respond to other treatments, researchers said. Going forward, further studies will include only children with the ALK mutations, Mosse said. Two of the neuroblastoma patients had a complete remission and eight had stable disease, or no worsening of the cancer. The most demonstrable response in neuroblastoma was seen at the higher doses, researchers said. In ALCL this is dramatic activity. In neuroblastoma there's still a lot of work to be done to identify the patients likely to benefit," Mosse said. The majority of the seven sarcoma patients experienced substantial benefit, ranging from tumor shrinkage to complete tumor regression, researchers found. Reporting By Bill Berkrot in New York; Editing by Michele Gershberg and Matthew Lewis