Lung Cancer Classifications

Squamous Cell Carcinoma

This is also called Bronchogenic or Epidermoid Carcinoma. (Epidermoid = skin-like, producing keratin) 

Squamous cell carcinoma comprises 25-38% of all lung cancers. 

The tumor arises centrally, along the major bronchi. It is considered an exophytic tumor because it’s a neoplasm that grows outward from an epithelial surface. It can end up blocking the bronchi, causing airway obstruction. 

Squamous cell carcinoma  is a local, regional disease. It spreads directly to surrounding lung parenchyma and local hilar lymph nodes. The lymph nodes can compress the major blood vessels in the lung parenchyma. 

The central, bronchiolar location of the tumor and the field effect of chronic smoking in the lung can be seen in this picture. The field effect is the localized spread of Squamous cell carcinoma  to certain lung areas based on the carcinogen’s effect.

The bronchiolar epithelium changes from respiratory columnar to squamous epithelium with keratin pearls. 

Adenocarcinoma

This is the most common form (40%) of lung cancer. One contributing factor to its prevalence is the increase of women smokers in the past 30-40 years because adenocarcinoma is also the most frequently diagnosed primary lung cancer in women. It is not corrrelated to smoking. 

Adenocarcinoma arises peripherally in the lungs and grows along the alveolar septa. It disseminates and metastasizes early. One way of metastasis (mentioned in class) is through coughing. The patient can cough and dislodge the tumor from its place of origin to push it into other areas of the lung. 
 

It can also be called scar carcinoma because it is sometimes associated with areas of lung scarring.  Breast and colon cancers can also present as lung adenocarcinoma, so it’s necessary to differentiate bronchiolar adenocarcinoma as either primary or secondary. Old pathology reports are useful for this. 

The prefix adeno- means gland, so an adenocarcinoma will contain mucin glands. You can histologically identify the glands by their lumens (they appear like white spaces). An excessive amount of mucus is produced; therefore, one diagnostic feature for adenocarcinoma is the presence of mucopolysaccharides in the lung. 

A tissue sample can be obtained by a needle biopsy, which can potentially lead to complications such as bleeding and pneumothorax. Air can get in from the outside or the tumor (malignant mesothelioma) can contaminate the bloodstream and grow on the tissue biopsy site.

Bronchoalveolar Carcinoma

Bronchoalveolar carcinomas are considered to be a subtype of adenocarcinomas. These are tumor cells that grow on top and along the alveolar septa. There is no alveolar destruction or stromal invasion. These tumors also produce mucus. 

Histologically, bronchoalveolar carcinomas are difficult to tell apart from viral pneumonia.

Small Cell Lung Cancer

It was also called Oat Cell Carcinoma because the researcher who discovered Small Cell Lung Cancer thought that the cancer cells reminded him of oats. 

This is the most rapidly growing lung cancer and accounts for 15-20% of all lung cancers. Since it’s not surgically treatable (resection = worse prognosis), different chemotherapy regimens are followed. Chemotherapy and radiation are alternative options to surgery but these have poorer prognoses for survival. 

Small Cell Lung Cancer can be staged as…

• Limited Disease – confined to the hemithorax; 1 radiation field
  • The survival prognosis is usually about 2 years.
• Extensive Disease – beyond the hemithorax
  • These people usually have a long smoking history.
  • 2/3 of patients are at the terminal stages of the disease when they first present with symptoms.
  • The survival prognosis is about 1 year.

Tumors arise from a central or mid-parenchymal location in the lung. 

Common sites of metastasis are

• Liver
• Brain
• Other lung regions

Despite their term as “small cell” lung cancer, these cells are actually 3x the size of lymphocytes. They are fragile cells, exhibiting nuclear molding (the cytoplasm of one cell conforms to another) and nuclear debris deposition due to necrosis. The tumor is growing so rapidly that it outgrows its blood supply, resulting in many non-viable tumors and necrosis. These tumors, derived from neuroendocrine cells, also produce polypeptide hormones, which are secreted by neurosecretory granules. Therefore, Small Cell Lung Cancer is also considered a high grade neuroendocrine carcinoma.

Small Cell Lung Cancer can present with many different paraneoplastic syndromes. Sit tight… because they’re coming up in a little bit!

Large Cell Lung Cancer

Large Cell Lung Cancer doesn’t have any distinguishing histologic features. It accounts for 4% of all lung cancers. The neuroendocrine variant of Large Cell Lung Cancer is identified with special stains (chromogranin and synaptophysin).

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