Clinical implications of the innovations in the primary tumour and metastasis of the 8^th edition of the TNM classification for lung cancer

The 8th edition of the tumour, node and metastasis (TNM) classification for lung cancer introduced two new categories to accommodate adenocarcinoma in situ (AIS)—Tis(AIS)—and minimally invasive adenocarcinoma—T1mi; subdivided T1 into T1a (≤1 cm), T1b (>1–2 cm) and T1c (>2–3 cm); and T2 into T2a (>3–4 cm) and T2b (>4–5 cm); reclassified tumours >5–7 cm as T3, and those >7 cm as T4; reclassified endobronchial location <2 cm from the carina and total atelectasis/pneumonitis as T2a; and reclassified invasion of the diaphragm as T4. Regarding metastasis, the 7^th edition M1a category remained the same, but M1b is now redefined to include single extrathoracic metastasis; and a new category, M1c, has been created for multiple extrathoracic metastases in one or in several organs. Tumours with worse prognosis than that assigned in previous editions, such as T3-4N2M0 and T3-4N3M0, were grouped in stages IIIB and IIIC, respectively. Stage IV was subdivided into IVA, for intrathoracic and single extrathoracic metastasis (M1a and M1b, respectively) and IVB, for multiple extrathoracic metastases (M1c). From the clinical point of view, these innovations will demand a more precise registration of tumour size, a thoughtful assessment of locally advanced tumours at multidisciplinary discussions, and a thorough search of extrathoracic metastases because the number of the metastatic sites has prognostic relevance and may influence therapy.