In preparation for the 8th edition of the TNM classification for lung cancer the International Association for the Study of Lung Cancer (IASLC) collected data on 94,708 cases of lung cancer diagnosed between 1999 and 2010, donated by 35 institutions in 16 countries. After exclusions, 77,156 remained for analysis: 70, 967 cases of non-small cell lung cancer (NSCLC) and 6,189 cases of small-cell lung cancer (SCLC). Analysis of the cases of NSCLC has allowed proposals for revisions to the T, N and M descriptors and TNM Stage groupings. Size remained an important determinant and a descriptor for all of the T categories. A new cut points at 1 and 4 cm have been proposed and as a result new T categories have been created: T1a ≤1 cm, T1b > 1 to 2 cm, T1c > 2 to 3 cm, T2a > 3 to 4 cm, T2b > 4 to 5 cm, T3 > 5 to 7 cm and T4 > 7 cm. However, measuring precise tumor size can be challenging since it is known that tumor gross size depends on whether the size measurement is performed on fresh or formalin-fixed specimen. In about 10% of cases, formalin fixation can cause down-staging of pathologic T category as a result of tumor shrinking. Tumors invading the diaphragm have been reclassified as T4, and tumors extending within 2cms of the carina without its invasion, or tumors associated with collapse or consolidation of the whole lung have been down-staged to T2. Tis and T1mi were introduced for adenocarcinoma in situ, squamous cell carcinoma in situ and minimally invasive adenocarcinoma, respectively. Visceral pleural invasion, defined as the involvement of its elastic layer, remains unchanged as T2 category, but specific analysis of visceral pleural invasion, showed that there is two types of invasion: PL1 where tumor invades beyond the elastic layer and PL2 where tumor invades pleural surface and that these two had different prognosis, PL2 being associated with the worst outcome. Elastic stains are recommended to clarify the status of visceral pleural invasion for cases in which initial hematoxylin-and-eosin-stained slides failed to show presence of invasion. Mediastinal pleura invasion disappears as a T descriptor. N categories remained the same as in 7th edition. 8th did not bring guidelines about the minimum number of lymph nodes that should be assessed for pathohistological analysis. In M descriptor category M1a retained, while M1b has been reassigned to describe a form of limited disease with a single metastatic deposit in one distant organ. A new category of M1c has been proposed and it is reserved for situations in which there are multiple metastases in one or more distant sites. Assessment of multifocal lung tumors and the distinction of synchronous primary tumors from intrapulmonary metastases represent an important problem as this decision significantly influences tumor staging, as well as treatment approach. Four different clinical presentation of lung cancer with multifocal lung involvement are described: second primary cancer, intrapulmonary metastasis, multifocal lung adenocarcinoma with ground glass/lepidic features, and pneumonic-type lung adenocarcinoma. The tumors are considered second primary tumor if it have clearly a different histology or have a different radiographic appearance, metabolic uptake growth pattern or different biomarkers. Each tumor is staged separately based on current TNM staging system. The nodules are considered to be intrapulmonary metastasis if exact matching breakpoints are identified by genetic hybridization or have similar clinical features such as radiographic appearance, growth pattern or significant nodal and systemic SPECIAL SESSION: DEPARTMENT OF PATHOLOGY, MEDICAL FACULTY, UNIVERSITY NOVI SAD, SERBIA 32 MATERIA MEDICA • Vol. 34 • Issue 1, suplement 1 • april 2018. metastasis. TNM staging depends on location of the nodule relative to the primary tumor site. If it is in the same lobe, the tumor is designated as T3, if it is in the same lung, but in different lobe as T4, and it it is in the contralateral lung as M1a. Tumors are considered multifocal lung adenocarcinoma if there are multiple subsolid nodules with at least one suspected or proven to be a cancer. Ground glass nodule <5 mm or lesion suspected to be AAH is excluded. T stage is based on highest T lesion with indicating the multiplicity. Tumor is categorized as a pneumonic-type adenocarcinoma if there is a diffuse pneumonic infiltrate or consolidation with regional distribution. Stage IA is divided into IA1, IA2 and IA3 to accommodate T1a, T1b and T1cN0M0 tumors. All N1 disease is staged IIB except for T3-T4N1M0 tumors which are stage IIIA. A new stage IIIC is created for T3-T4N3M0 tumors and stage IV is divided into IVA (M1a and M1b) and IVB (M1c). In conclusion, multi-disciplinary approach and the close cooperation among medical and radiation oncologists, pulmonologists, surgeons, radiologists and pathologists is important in properly staging of lung cancer as well as, in treatment plans.

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