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Lung cancer and mesothelioma: Pathology review
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Two people came to the clinic one day. First is a 65-year-old named Alex, who presents with a two-month history of dry, persistent cough and weight loss of around 7 pounds without dieting. He also says he coughs up blood sometimes but denies fever, dyspnea, sore throat, rhinorrhea or any chest pain. Alex has a history of asthma and hypertension, and smoked 1 pack of cigarettes daily for 45 years. On examination, his breath sounds are diminished at the right lung base.
The other individual is Clara, who’s an 80-year-old retiree. Before her retirement, Clara was a construction site supervisor. She complains of increasing shortness of breath, which started ten months ago, and new onset of myalgia located on the right side of her chest. Physical examination reveals decreased breath sounds in the right lung base along with dullness to percussion. Chest X-rays were ordered for both people. In Alex’s case, it showed a single, coin-like lesion on the right lung base. Clara’s scan showed pleural effusion, irregular pleural thickening, and two ivory white, calcified pleural plaques at the base of her right lung.
Both people have cancer involving the lung. But first, a bit of physiology. Lining the airways are several types of epithelial cells that serve multiple functions. These include ciliated cells that have hair-like project called cilia that work to sweep foreign particles and pathogens back to the throat to be swallowed. Another type, called goblet cells secrete mucin to moisten the airways and trap foreign pathogens. There are also basal cells that are thought to be able to differentiate into other cells in the epithelium, club cells that act to protect the bronchiolar epithelium, and neuroendocrine cells that secrete hormones into the blood. On the outside, the lungs are covered by the mesothelium which consists of the parietal pleura and the visceral pleura. Between them, there’s the pleural space, where the fluid produced by the epithelial cells is released, which acts as a lubricant to allow the layers to slide effortlessly against each other during respiratory movements.
Now, let’s begin with lung cancer. The two most common types are small cell lung cancer and non-small cell cancer, both sharing common pathophysiology. Cells of the lungs can undergo mutations that cause them to divide uncontrollably and replace the normal healthy lung tissue. Eventually these cells will form a tumor. To supply it, new blood vessels also develop and this is called angiogenesis. Sometimes the tumor can metastasize and spread via blood vessels or lymphatics and establish secondary sites throughout the body. Particularly at risk for lung cancer metastasis are the mediastinum and hilar lymph nodes because of their proximity to the lungs, so remember this as it’s very high yield! Other common sites include the liver, adrenal glands, bones, and brain.
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