Novartis AG's drug Glivec, which has dramatically improved survival prospects for some cancer patients, can interfere with bone development, according to US researchers.

Results of a small study published in the New England Journal of Medicine found the drug could inhibit bone formation and resorption -- a process known as bone remodelling.

The side effect was detected by Dr Ellin Berman and colleagues at the Memorial Sloan-Kettering Cancer Center in New York after some patients on the drug developed low levels of serum phosphate, a mineral important in bone formation, said report.

The new finding, however, was based on just 16 patients with low mineral levels and the full significance of the discovery has yet to be ascertained.

Glivec, or Gleevec as it is known in the United States, was approved five years ago and has grown to be Novartis's second biggest selling product, with sales last year of $2.2 billion.

The drug has transformed life expectancy for people with chronic myeloid leukaemia (CML) and a type of stomach cancer called GIST. Five years of use shows patients taking Glivec have a 90 per cent survival rate, says the report.