Patients with certain complex cancers fare better under the care of doctors and hospitals that do the most of that kind of surgery, a new review of studies finds.

The exact reasons for the better outcomes are unclear, according to an article in the British Journal of Surgery, but the correlation between high volume and better outcomes, especially in pancreatic, esophageal, gastric and rectal cancers, was consistent across most studies.

Previous studies have shown similar results in patients treated for heart attacks, breast cancer and other diseases; those hospitals that treat a higher volume of chronically ill patients have lower mortality rates. Again, the reasons for the disparities in outcomes are unclear. Although some researchers postulate that "practice make perfect," other experts believe that physicians tend to refer their sickest patients to medical centers that have an outstanding reputation.

"All studies showed either an inverse relationship, of variable magnitude, between provider volume and mortality," according to authors S.D. Killeen and colleagues of the Cork University Hospital and University College in Ireland. "The majority of clinical studies revealed a statistically significant correlation between volume and outcome; no study demonstrated the opposite relationship."