Page 394 - Concise Pathology for Exam Preparation ( PDFDrive )

13 The Lung 379

Classification of malignant epithelial tumours

1. Histological classification
(a) Squamous cell carcinoma (papillary, clear cell, small cell and basaloid)
(b) Adenocarcinoma (most common)
(i) Minimally invasive adenocarcinoma (nonmucinous and mucinous)
(ii) Lepidic, acinar, papillary, solid (according to pattern of arrangement of
tumour cells)
(iii) Mucinous adenocarcinoma
(c) Small cell carcinoma
Combined small cell carcinoma
(d) Large cell carcinoma: Large cell–neuroendocrine carcinoma
(e) Adenosquamous carcinoma
(f) Carcinomas with pleomorphic, sarcomatoid or sarcomatous elements
(g) Carcinoid tumour: Typical and atypical
(h) Carcinoma of salivary gland origin
(i) Unclassified carcinomas
2. Therapy-based classification
(a) Small cell carcinoma (aggressive; show a high initial response to chemotherapy)
(b) Non–small cell carcinoma (have a better prognosis than small cell carcinomas)

Epidemiology

• Adenocarcinoma is the most common lung carcinoma in females; incidence of adeno-
carcinoma has increased over the past few years (increase in incidence is thought to be
due to increase in the number of female smokers).
• Strongest relationship with smoking is seen in squamous cell and small cell carcinoma.
• Bronchogenic carcinoma is the most frequently fatal malignancy with a peak incidence
between 40 and 70 years.

Aetiology and Pathogenesis
1. Role of tobacco smoking:
(a) Invariable statistical association with:
• Amount of daily smoking and tendency to inhale
• Duration of habit (heavy smokers smoking more than 40 cigarettes/day for many
years have a 20-fold increased risk)
Eight percent incidence of lung carcinoma occurs in smokers. Cigar and pipe smoking
associated with less risk.
Note: Other smoking-associated cancers: cancer of lip, tongue, floor of mouth, pharynx,
larynx, oesophagus, urinary bladder, pancreas and kidney
(b) Documentation of precursor histological changes (hyperplasia and dysplasia) in
lining epithelium of respiratory tract in smokers.
(c) Experimental work has revealed presence of more than 1200 harmful substances
found in tobacco smoke, eg,
(i) Initiators like polycyclic aromatic hydrocarbons (benzopyrene)
(ii) Promoters such as phenol derivatives
(iii) Radioactive elements—polonium-210, carbon-14 and potassium-40
(iv) Arsenic, nickel and molds
Not all people exposed to tobacco smoke, however, develop lung cancer. It is therefore
hypothesized that the mutagenic effect of tobacco smoke is dependant on genetic
variants (the procarcinogens present in tobacco smoke are converted to carcinogens
by P-450 monooxygenase enzyme. Specific P-450 polymorphisms have an enhanced
ability to activate them, making smokers with these genetic variants more susceptible
to lung cancer).
2. Industrial hazards associated with lung carcinoma:
(a) Radiation
(b) Uranium (miners)

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