1 Histologic Classification of Lung Tumours

Most lung cancers arise from the bronchial walls rather than the lung alveoli parenchyma. Approximately 80% of lung cancer cases have non-small cell (NSCLC) pathology and 20% have small cell carcinoma (SCLC). Currently, about 40% of NSCLC cases are adenocarcinoma subtypes and about 40% are squamous tumours. The remaining NSCLC cases have large cell anaplastic, less common subtypes and carcinoma NOS. For management decisions, NSCLC including squamous (epidermoid), adenocarcinoma and large cell anaplastic carcinoma are considered together.

Small cell carcinoma includes classic "oat cell" and intermediate size subtypes. There are no convincing clinical data to support treating classic or "oat cell" subtype of small cell carcinoma different than the intermediate subtype. Combined small cell and NSCLC is commonly managed with the SCLC treatment paradigm but non-small cell pathological elements are associated with greater treatment resistance and less durable remissions.

The World Health Organisation's histologic classification of carcinoma of the lung is as follows:

1. Dysplasia, carcinoma in situ
2. Squamous cell carcinoma
3. Small cell carcinoma
1. Small cell carcinoma 
2. Intermediate cell type carcinoma
3. Combined small cell carcinoma
4. Adenocarcinoma
1. Acinar adenocarcinoma 
2. Papillary adenocarcinoma 
3. Bronchioloalveolar carcinoma
4. Solid carcinoma with mucus formation
5. Large cell carcinoma 
6. Adenosquamous carcinoma 
7. Carcinoid tumour
1. Classic carcinoid
2. Atypical carcinoid
8. Bronchial gland carcinomas
9. Others

Key References 

1. Colby TV, Koss MN, Travis WD. Atlas of Tumor Pathology: Tumors of the Lower Respiratory Tract. Armed Forces Institute of Pathology, Washington DC, 1994  

2. Travis TV, Colby TV, Corrin B, Shimosato Y, Brambilla E. Histologic and graphical text slides for the histologic typing of lung and pleural tumors. In: World Health Organisation Pathology Panel: World Health Organization. International Histological Classification of Tumors. 3rd ed. Springer Verlag, Berlin, 1999 (page 5).

2 Diagnostic Pathology

Definitive Diagnosis of Lung Cancer

A full history and physical examination should precede any investigation. Because clinical lung cancers are sometimes shown to be a benign process and because of the difference in treatment for non-small cell and small cell lung cancer, histological or cytological verification of the diagnosis should be obtained.

Diagnostic procedures should be tailored to the individual patient and may include: 

1. Review of old chest X-rays to exclude a long-standing benign lesion or determine the rate of progression of a malignant lesion.  
2. Sputum cytology: three early morning specimens of sputum should be collected in seventy percent alcohol; post-bronchoscopy cytology when the patient is coughing vigorously, may be helpful.  
3. Bronchoscopy, biopsy of endobronchial lesions, brushings and washings, post-bronchoscopy sputum cytology.  
4. Mediastinoscopy: to exclude inoperable metastases in mediastinal lymph nodes.  
5. Percutaneous fine needle biopsy in selected cases.  
6. Excisional or needle biopsy of readily accessible secondary deposits

Once the diagnosis of non-small cell lung carcinoma has been established, steps are taken to stage clinically and assess the patient for operability. Small-cell lung carcinoma has considerably different staging, treatment and prognostic characteristics from non-small cell lung carcinoma and will be discussed in a later section (5.3.2).

Pathological Evaluation of Resection Specimens
The specimen should be received fresh. Frozen sections of the planned bronchial margin and nodes at this site may be requested. The specimen is inflated with fixative (either endobronchially or via a large bore needle inserted transpleurally into each segment) and allowed to fix in the inflated state overnight. Complete slices are then made in the fixed specimen in the desired plane to correspond to a P-A or lateral chest X-ray or CT scan.

Assessment of T Status 

Peripheral tumour 

1. Tumour size in three dimensions is noted.  
2. Segment location and distance from pleura is noted.  
3. Presence of adherent parietal pleural or pericardium is noted.

Central tumour 

1. Tumour size in three dimensions is noted.  
2. Location of the involved bronchus, gross depth of invasion, degree of luminal occlusion, distance from pleura are all noted.

Assessment of N Status 
In a pneumonectomy specimen, the nodes around the main bronchus are N2 nodes and should be assessed separately. In all specimens, the nodal station of grossly positive nodes should be specified.

Minimum Sections 

1. Bronchial resection margin.  
2. Three or four sections of tumour to include its relationship to pleura and/or parent bronchus; for peripheral tumours less than 3 cm, the entire pleural-tumour interface should be processed.  
3. Lymph nodes from around the bronchial resection margin should be submitted separately from other nodal tissue.  
4. The presence of grossly positive nodes must be verified histologically.  
5. If no grossly positive nodes are identified, all nodal tissue should be processed to exclude microscopic metastases.