- Describe the histopathology of the mass lesion. What is the diagnosis? What features do you use to make this diagnosis?
There are cords and sheets of large cells intertwining with whorls of desmoplastic fibrous tissue. The large cells are arranged in a mosaic pattern, and have abundant eosinophilic cytoplasm and large nuclei. The nuclei show the malignant features of hyperchromasia, irregular nuclear border, chromatin clumping, and numerous mitoses. This is a moderately differentiated squamous carcinoma. To make this diagnosis you need to see keratinization and/or keratin pearls, and/or intercellular bridges. In this case, bridges are fairly easy to find, and there are occasional individually keratinized cells, though keratinization is not a prominent feature in this case.
- Where does this lesion usually arise? What is the hypothesized mechanism of carcinogenesis?
Squamous carcinomas are most often central, arising in the mainstem, 1st, 2nd, or 3rd order bronchi. The mechanism of carcinogenesis is thought to be a response to a carcinogen, most often smoking, in the bronchial epithelium resulting first in metaplasia from columnar to squamous, going on to cytologic atypia and then carcinoma.
- What might you see (image 4.6) in the parenchyma of the lung behind the lesion?
Since bronchogenic carcinoma often arises in bronchi, there is often bronchial plugging. This may lead to bronchopneumonia in the lung behind the cancer, or to endogenous lipid pneumonia. In the first case you would see acute inflammation, in the second numerous large lipid laden macrophages in the alveolar space.
