B.C. health officials say cancer may have been overlooked in a half-dozen patients whose CT scans were analyzed by unqualified hospital staff last year.

The scans were taken by a full-time radiologist in Powell River between April and October and a part-time radiologist who practiced in the Fraser Valley last August and September. Neither is currently practicing in B.C.

The Ministry of Health says the pair lacked "either the appropriate credentials or experience" to properly interpret the results of both ultrasounds and CT scans -- and it appears several cancer diagnoses were missed as a result.

"Discrepancies have been discovered," said Dr. Nigel Murray, president of Fraser Health Authority. "We are finding some cases were false positives."

The radiologists saw nearly 3,400 patients, all of whom are being notified of the situation. Reviews by Vancouver Coastal Health and Fraser Health indicate patient care was not compromised in the majority of cases, but roughly 140 require further investigation.

The part-time radiologist was also involved in about 200 cases in the Cranbrook area, but doctors say none of those patients' care was affected.

"I want to apologize for the stress and anxiety this may cause," Health Minister Colin Hansen said, adding that doctors would ensure patients quickly receive any necessary follow-up tests and care.

The ministry has launched a two-part investigation into the problem, beginning with an immediate 30-day probe to ensure all radiologists in the province have proper credentials.

The second part will analyze the credentialing process and the health authorities' response to the problem. The results of both probes will be made public within six months.

With a report from CTV British Columbia's Shannon Paterson