Lung Cancer

Introduction
Lung cancer is the leading cause of cancer death in the United States with approximately 222,520 new cases and 157,300 deaths expected in 2010.

Challenges
It can be difficult to determine if the tumor has invaded the bronchus on CT which would change it from T2 to T3. It can be difficult to discern tumor from post obstructive pneumonitis or consolidation.

Controversy
In a 35 year retrospective study of 2952 patients who underwent pulmonary resection for non-small cell lung carcinoma there were no significant differences in survival between the Ib, IIa, IIb, IIIb, and IV clinical stages.

Much controversy exists about the role of intrapulmonary metastasis, whether they should be classified as T4 (stage IIIB) when in the same load and whether upstaging them based off of this finding eliminates the possibility of potentially respecting the tumor.

Nodal skip metastases, particularly the presence of N2 disease without N1 disease occur most frequently in upper lobe tumors and have a more favorable outcome.

There are two lymph node maps being currently used:


 * 1) Naruke map
 * 2) Mountain-Dresler-American Thoracic Society map

They differ mainly on the treatment of the designation of lymph nodes in the sub-carina space along the inferior border of the main stem bronchus. The Naruke map designates these lymph nodes as N1 while the Mountain-Dressler-American Thoracic Society map uses them as N2.

History
Historically the tumor, nude, metastasis staging system for lung cancer was first proposed in 1973 and were based on a database of 2155 cases of histologically proved bronchogenic carcinoma. At that time the staging manual included a case distribution which represented 58% squamous cell carcinoma.

Basics
The purpose of staging is to:

The tumor, node, metastasis (TNM) staging system is the most popular and classifies a tumor based off its anatomic extent.
 * 1) standardize communication between treatment centers
 * 2) enable classification of patients according to the tumor characteristics
 * 3) stratify the patients based on proposed treatment approaches
 * 4) allow evaluation of treatment strategies
 * 5) define the prognosis of the patient

The use of PET/CT, endoscopic ultrasonography, endobronchial ultrasound, endoscopic ultrasound guided fine-needle aspiration, and endobronchial ultrasound-guided trans-bronchial needle aspiration has made minimally invasive tumor staging possible.

The staging system is continually changed to reflect differences in Kaplan-Meier survival estimates of specific breakpoints in anatomic disease.

TNM-7 staging changes
There were survival differences in patients with pathologically staged size cut points at two, three, five, and 7.3 cm. Tumors 2 cm or smaller are now classified as as T1a and tumors between 2 cm and 3 cm are classified as T1b.

Patients with nodules on the same lobe would have been classified as having T4 disease however their disease has survival rates in line with stage T3 disease therefore the tumor, node, metastasis staging system has changed to now make them T3 disease.

Patients with nodules in a different lobe than the primary were previously classified as having metastatic disease, however due to them having similar survival rates as those with T4 disease the tumor, node, metastasis staging system has changed now reclassify them as T4 disease.

Pleural dissemination was moved from the T4 category to the new M1a category to reflect its true nature as a intrathoracic metastatic disease.

The M1 category was divided into M1a and M2a. M1a includes intrathoracic metastasis and includes pleural dissemination and contralateral pulmonary nodules while M2a includes extra thoracic metastasis.

To reconcile the Naruke nodal maps and the Mountain-Dressler-American Thoracic Society nodal map the existing nodal stations were grouped into six anatomic zones: upper, aorta pulmonary, subcarinal, lower, hilar, and peripheral. The hilar and peripheral zones represent N1 disease, and the upper, aortopulmonary, subcarinal, and lower zones represent N2 disease.

The reclassification of the same lobe nodules from T4 to T3 cause the tumors to be classified as N0M0 which means they are now downstage to IIB from IIIB. The designation of T2 tumors larger than 7 cm as T3 caused the upstaging of these tumors from stage IB to stage IIB.

Types
The increased rate of adenocarcinoma has been attributed to the use of filtered, low tar, nicotine cigarettes which results in the deposition of carcinogens (N-nitrosamines) in the peripheral lung parenchyma of smokers.
 * 43% = adenocarcinoma
 * 23% = squamous cell carcinoma
 * 34% = others