USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 40-year-old man comes to the office because of shortness of breath, increasing fatigue, lack of appetite and subsequent weight loss for the past 3 months, during which time he has lost 15-kg (33.1-lb). His temperature is 37.6°C (99.6°F), pulse is 80/min and respiratory rate is 16/min. Laboratory studies show a hemoglobin concentration of 10.7 g/dL. He has had lobar pneumonia 4 years ago, and he has been working as a ship builder for the past 10 years. Chest CT is obtained. Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
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.