The Eighth Edition of the Tumor, Node, and Metastasis Classification of Lung Cancer

T Descriptors

The T component of the classification is complex to analyze because it has many descriptors: tumor size, endobronchial location, atelectasis/pneumonitis, and invasion of various anatomic structures surrounding the lung. For their analyses, the prognostic impact of each descriptor was analyzed individually in five different populations of patients: three with pathologically staged tumors (pT1–4 N0 M0 completely resected [R0]; pT1–4 any N M0 R0; and pT1–4 any N M0 any R, i.e., including resections with microscopic [R1] and macroscopic [R2] evidence of residual tumor) and two with clinically staged tumors (cT1–4 N0 M0 and cT1–4 any N M0). Additional univariate and multivariate analyses were performed after adjustment by histopathologic type, geographical region of origin, age, and sex. These analyses generated multiple survival curves that were closely analyzed to see if the different descriptors were properly assigned to their T category. The results of these analyses can be summarized as follows:

• The 3-cm landmark still separates T1 from T2 tumors.

• Tumor size, analyzed at 1-cm intervals, has more prognostic impact than previously shown in past editions of the TNM classification. From less than or equal to 1-cm to less than or equal to 5-cm tumor size, every centimeter counts and separates different T categories.

• The prognosis of tumors greater than 5 cm to less than or equal to 7 cm was similar to that of T3 tumors.

• The prognosis of tumors greater than 7 cm was similar to that of T4 tumors.

• The prognosis of tumors with endobronchial location less than 2 cm from the carina (a T3 descriptor in the 7th edition) was found to be similar to that of their T2 counterparts (endobronchial location >2 cm from the carina).

• The prognosis of tumors with total atelectasis/pneumonitis (a T3 descriptor in the 7th edition) was found to have a T2 prognosis, similar to that of tumors with partial atelectasis/pneumonitis.

• The prognosis of tumors with invasion of the diaphragm (a T3 descriptor in the 7th edition) was found to be similar to that of T4 tumors.

• The invasion of the mediastinal pleura was rarely used as a unique descriptor.

Based on the aforementioned findings, the recommendations for changes in the T categories are as follows:

• Subdivide T1 into three new subcategories: T1a (≤1 cm), T1b (>1 cm but ≤2 cm), and T1c (>2 cm but ≤3 cm).

• Subdivide T2 into two new subcategories: T2a (>3 cm but ≤4 cm) and T2b (>4 cm but ≤5 cm).

• Reclassify tumors greater than 5 cm but less than or equal to 7 cm as T3.

• Reclassify tumors greater than 7 cm as T4.

• Reclassify tumors with endobronchial location less than or equal to 2 cm from the carina, but without involvement of the carina, as T2.

• Reclassify tumors with total atelectasis/pneumonitis as T2.

• Reclassify tumors with invasion of the diaphragm as T4.

• Delete the invasion of the mediastinal pleura as a descriptor.

When survival is analyzed according to these new T descriptors, survival curves separate well and do not cross over. All survival differences are significant and there is a clear difference between T3 and T4 that was not seen in the seventh edition ( Fig. 25.1 ).

Visceral pleural invasion, defined as the invasion of its elastic layer, is well assigned to the T2 category ( Fig. 25.2 ). There are survival differences between PL1 and PL2, but these are only identifiable at pathologic staging, so they cannot be used to modify the present T2 descriptor based on the extent of visceral pleural invasion. However, they are useful to refine postoperative prognosis in those patients with resected tumors in which visceral pleural invasion is identified. Because visceral pleura involvement impacts prognosis, the use of elastic stains is emphasized again in the eighth edition of the TNM classification of lung cancer, if it is not evident on hematoxylin and eosin stains.