The chances of surviving many types of cancer are better than statisticians thought, according to a new way of calculating the odds that takes into account improvements in treatment.
The new technique, outlined this week in The Lancet medical journal, separates recent patients from those who received less advanced treatment in years past.
The method is increasingly being adopted in Europe, where it was first proposed. American experts are starting to evaluate its merits. The new approach, proposed by German epidemiologist Hermann Brenner, is commonly used in other areas of medicine, such as predicting life expectancy.
In the Lancet study, Brenner analyzed more than 1.7 million patients recorded in the U.S. National Cancer Institute database.
He found that the new method estimates American breast cancer patients had a 71 percent chance of surviving 15 years, while the conventional approach put the chance at 58 percent.
Similarly, the 15-year survival rate for American men with testicular cancer was 91 percent, compared to 86 percent with the old method.
The survival rate for ovarian cancer five years after diagnosis was 55 percent with the new method, compared with 49 percent previously.
The conventional method of estimating cancer-patient survival, called the cohort approach, estimates the chances of surviving a particular cancer for, say 10 years, by looking at what has happened to patients diagnosed between 1990 and 2000.
"Cohort estimates are generally not appropriate for predicting the survival of newly diagnosed patients since the estimates are heavily weighted toward the survival experience of patients diagnosed many years in the past," said Paul Dickman, a professor of biostatistics at the Karolinska Institute in Stockholm, Sweden, who is a proponent of the new method but was not connected with the latest study.
The new approach, called period analysis, is based only on recent years - for example, on patients who were alive and under follow-up during the year 2000.
Henrik Moller, a professor of cancer epidemiology at the London School of Hygiene and Tropical Medicine, is a fan of Brenner's approach.
"Cancer survival tends to improve, very gradually, but very certainly," said Moller, who is also director of research at the Thames Cancer Registry in London. "This technique (picks up) improvements in survival better than the old one."
Timo Hakulinen, director of Finland's cancer registry, tested both methods. He thought the new method might overestimate survival, "but that turned out not to be the case. There was not a single (cancer) site where it was too optimistic," Hakulinen said. "It has proven to be surprisingly good."
Hakulinen cautioned the new method is more prone to give wrong results if the database is not of good quality.
Brenda Edwards, associate director of the surveillance research program at the U.S. National Cancer Institute, said her team needs more convincing.
"I have not had my first-rate methodologists go in and look at it to compare and contrast the attributes of this approach versus other approaches that we've taken here in the United States," Edwards said. "I view it as just another technique that we will have to look at more closely."
By Emma Ross