USMLE® Step 1 style questions USMLE
A 65-years-old man comes to the clinic due to the gradual onset of chest pain, dyspnea, and night sweats for the past 2 months. He also reports a nagging non-productive cough for which he tried over the counter cough syrup with no relief. He does not drink alcohol but has smoked a pack of cigarettes daily for the past 40 years. Temperature is 37.0 °C (98.6 °F), pulse is 80/min, respirations are 20/min, and blood pressure is 135/85 mmHg. On physical examination, decreased air movement and unilateral dullness to percussion at the lung base are noted on the left side. Computed tomography is obtained and shown below:
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This patient’s condition is most likely associated with which of the following occupational exposures?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS, Yifan Xiao, MD, Vincent Waldman, PhD, Brittany Norton, MFA
Mesothelioma is an aggressive cancer that attacks the mesothelium, which is a thin membrane made of epithelial cells that lines all of the body’s organs as well as body spaces like the thoracic cavity and abdominal cavity.
Mesothelioma most often develops in the lining of the lungs and pleural cavity, and is well known for its association with the carcinogen asbestos.
In fact, the late Hollywood actor Steve McQueen is well-known for having developed mesothelioma after years of asbestos exposure while in the military.
The vast majority of mesothelioma cases stem from asbestos exposure.
Asbestos is a mineral that was widely used as construction material in everything from paint to insulation to roofing tiles because it has strong fibers that were resistant to fire and served as good insulation.
Asbestos fibers are jagged in shape, and extremely tiny - about 500 times finer than a human hair.
If those tiny asbestos fibers get inhaled over time, they make their way into the interstitial space of the lungs and then slowly make their way over to the epithelial cells of the visceral or parietal pleura - both of which are layers of mesothelium.
The microscopic, jagged asbestos fibers are so small that they can get tangled up with the cell’s chromosomes.
At that point, they can damage the DNA causing a variety of mutations, which ultimately allow those epithelial cells to divide uncontrollably, turning into a tumor.
Over time, small cancerous growths called mesothelial plaques start to cover the visceral pleura over the lungs and the parietal pleural under the chest wall.
Interestingly, these growths start to express a lot of calretinin, a calcium-binding protein, involved in regulating calcium levels within the cell - this is something that helps to distinguish mesotheliomas from other types of tumors.
In addition to affecting the lungs and pleural lining, asbestos fibers can also end up in the stomach if saliva containing the material or mucus from the airways is swallowed.
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