Primary tumours of the lung and pleura - benign & malignant. Histological and macroscopic forms
Main types of primary malignant lung tumours:
- Non-Small-Cell lung cancer types
- Adenocarcinoma (40%)
- Squamous Cell Carcinoma (25-30%)
- Large cell carcinoma (10-15%)
- Small Cell Lung Cancer (Small Cell Carcinoma - 15-20%)
Adenocarcinoma
- Genes that mutate to allow adenocarcinoma development: EGFR, ALK, ROS, KRAS
- Smoking is still the main risk factor, but it is also the most common type in non-smokers, especially women.
- May occur as central lesion, but more commonly peripherally located
- They grow slowly, and form smaller masses than other subtypes, but metastasise earlier
- Histological form may be acinar (gland-forming), papillary, mucinous or solid type.
- Precancerous lesion is adenocarcinoma in situ, with hyperplasia and fibrosis of alveolar walls
- Diagnosis through direct observation of enlarged glands or increased mucin production. If this is not observed, should perform immunohistochemistry to observe TTF antibodies
Squamous Cell Carcinoma
- Gene that mutates to allow carcinoma is TP53
- Main etiological cause is smoking (99% of patients are smokers)
- Lesions tend to arise centrally in major bronchi, close to the hilum, causing central necrosis and cavitation
- Often produce productive cough, the sputum of which may contain cancerous cells which can be examined under a microscope.
- SCC’s produce keratinisation of cells, with keratin pearls on histological examination. These prove the diagnostic gold standard, without this, observe antibodies P40 and cytokeratin 5 & 6.
- Pre cancerous lesion is squamous metaplasia or dysplasia of bronchial epithelium, which then progresses to carcinoma in situ.
Gross: central squamous cell carcinoma. A firm grey-white tumour involves the main bronchi at the carina and has spread to the subcarinal lymph nodes; the surrounding lung is black with smoker's pigment.
Image: “Squamous cell carcinoma (3950818822)” by Yale Rosen from USA, CC BY-SA 2.0, via Wikimedia Commons.
Large Cell Carcinoma
- Can appear in any part of the lung, presents as a non-productive cough with weight loss
- It is diagnosis by exclusion, as the tumour cells lack the characteristics that would define them as other non-small cell carcinomas or small cell carcinomas.
- Comprises 5-10% of all lung cancers
Small cell carcinoma
- Genes that mutate are TP53, Retinoblastoma gene (RB) and Transcription factor coder MYC
- Lesions generally located centrally, but can be peripheral
- Typical growth is subepithelial, and so invisible underneath the mucosa of the bronchi, diagnosis may have to be via a blind biopsy
- Often metastasizes into the mediastinum, with enlarged lymph nodes present
- Highly proliferative tumour, surgery not an option, chemotherapy and radiotherapy are prefered