New IASLC lung cancer staging system expands categories

Jason Akulian, MD, MPH, FCCP
Jason Akulian, MD, MPH, FCCP

The eighth edition of the TNM Stage Classification of Lung Cancer brings important changes from the seventh edition, published in 2012. Look for new tumor measurement criteria and location as the defining feature for some tumors, experts in a Tuesday session explained.

“This new edition for nonsmall cell lung cancer (NSCLC) is based on a sophisticated analysis of more than 70,000 patients with NSCLC,” said Jason Akulian, MD, MPH, FCCP, assistant professor of medicine and director of interventional pulmonology at the University of North Carolina School of Medicine. “We have more granularity in staging with this larger database.”

What hasn’t changed is need for a staging system that allows clinicians worldwide to describe and discuss tumors clearly and consistently regardless of patient characteristics, geographic region, or treatment modality.

“Stage classification is a nomenclature to describe the anatomic extent of disease and nothing more,” said Frank Detterbeck, MD, FCCP, chief of thoracic surgery and surgical director of thoracic oncology at Yale School of Medicine. “It is not a treatment model or a prognostic prediction model.”

The fundamental structure of stage classification has not changed from earlier editions: T for characteristics of the primary tumor, N for nodal involvement and M for distant metastasis. T, N, and M categories that exhibit similar behavior are classified in stage groups from IA1 to IVB.

The primary T groups, T0 to T4, have not changed, but more intermediate subcategories in the eighth edition provide greater granularity. The most important changes from the seventh edition to the eighth edition are noted below.

Tumor size is determined by the largest dimension of the solid portion of the tumor based on computed tomography using one millimeter slices, or the invasive portion. If there are several areas of solid and invasive tumor, multiply the largest total dimension, including the ground glass or lepidic components, by the proportion that is solid by imaging or invasive by histology. The largest total dimension, including the ground glass or lepidic components, should also be noted:

  • Tumor size is now subdivided by one centimeter increments up to five centimeters.
  • Tumors of three centimeters or less are T1, subdivided by size into T1a, b, and c.
  • Tumors greater than three centimeters and up to five centimeters are T2, subdivided by size into T2a and b.
  • Tumors greater than five centimeters up to seven centimeters are T3.
  • Tumors greater than seven centimeters are T4.
  • Tumors involving the main stem bronchus or causing lung atelectasis or obstructive pneumonitis are classified as T2 regardless of distance from the carina or whether they cause partial or total lung atelectasis.
  • Tumors that involve the diaphragm are T4.
  • The N groups remain unchanged, N0 to N3, no regional node metastasis to metastasis in contralateral mediastinal, hilar, or supraclavicular nodes.
  • The M groups have expanded with the addition of subgroups. Tumors that involve a single distant, e.g. extrathoracic, site are classified as M1b. Tumors that involve multiple distant sites are classified as M1c.

While survival rates have improved by about 30% from 1990 to 1999 period, stage is still not a key prognostic factor for most lung cancers, Dr. Detterbeck noted. Genomics, patient characteristics, geography, treatment modalities, and other factors all play more important roles.

Another key change is the focus on using thin-cut CT imaging for staging. Historically, five-millimeter cuts were used for diagnosis, noted M. Patricia Rivera, MD, FCCP, professor of medicine at the University of North Carolina School of Medicine. These thick cuts can miss important detail.

“Scans should have thin cuts, two millimeters or less,” she said. “You cannot rule out the presence of solid masses without thin-cut imaging.”