Long Beach, Calif. ? Thousands more lung cancer patients each year could be offered surgery or other aggressive therapy under a new system that classifies many tumors as more treatable than in the past.

It is the first big overhaul of a decades-old method used to predict survival and help determine whether a lung cancer patient will have surgery, chemotherapy or be treated at all.

The new guidance is to be presented at a conference of lung cancer specialists in Seoul, South Korea, that starts today. It is expected to be adopted by policy-making groups in the next year.

Lung cancer is the world’s top cancer killer, claiming 1.3 million lives each year. In the United States, 213,380 new cases and 160,390 deaths from the disease are expected this year.

In treating it, doctors use a formula called tumor staging. It is based on a tumor’s size, how far it has spread and other factors to predict a patient’s survival odds and to guide treatment.