Mesothelioma: Putting Together the Puzzle Pieces for an Accurate Diagnosis

Malignancies involving mesothelial cells that line the body's serous cavities and internal organs, including the pleura, pericardium, peritoneum, and tunica vaginalis, are known as malignant mesothelioma. Asbestos is the principal carcinogen implicated in the pathogenesis of malignant mesothelioma. Despite known immunohistochemical markers and other diagnostic techniques, the histologic diagnosis of malignant mesothelioma is not always straightforward.

A complete medical history, including the likelihood of asbestos exposure, should be taken into consideration by the pathologist when confirming or excluding mesothelioma or other asbestos-related pulmonary conditions. Understanding the possible signs, symptoms, and nature of pulmonary malignancy related to inhalation of asbestos fibers, can reduce the time to diagnose them and potentially contribute to the improved survival rate.

Malignant pleural mesothelioma—the most common type, representing about 75% of all mesothelioma cases—is a fast-growing tumor with a high mortality rate and overall survival of less than 1 year. General oncologists typically see only a few cases of mesothelioma through the course of a career, so they are not likely to recognize the differences between pleural mesothelioma and lung cancer signs, symptoms, and test results. Delayed diagnosis or misdiagnosis can happen even to highly experienced and competent doctors, because of the unusual nature of the symptoms and/or the multifaceted complexity of the disease.

Some of the most common reasons why a general doctor or oncologist may misdiagnose mesothelioma are:

• Complexity. Although mesothelioma has been extensively investigated at molecular levels during the last four decades and its connection with asbestos exposure is undeniable, there are many aspects that remain a challenge for the medical community.
• Low prevalence. Mesothelioma is extremely rare, unique, and has only been diagnosed in a small number of cases, which makes it an incredibly challenging cancer for doctors to diagnose. This aggressive form of cancer can appear to be many other types of cancer – both in symptoms and at the microscopic level.
• Similarities in observable masses. Mesothelioma develops small, interconnected tumors that eventually blend the boundaries between healthy and cancerous tissue, making it much more difficult to target. In most cases, pleural mesothelioma has been confused with several types of lung cancer—most notably, non-small-cell lung cancer. The ability to differentiate between malignant mesothelioma, benign asbestos-related pleural diseases, or pleural metastases requires multimodal evaluation, such as B-Reader evaluation. B-Readers are physicians qualified by the National Institute for Occupational Safety and Health (NIOSH) to read asbestos-related X-ray films. Practically, a B-reader evaluates chest X-rays to see if there are any changes that point towards diseases induced by inhalation of particles such as silica and asbestos.
• The long latency period. Inhaling asbestos causes microscopic fibers to become lodged within lung tissue, leading to scarring and inflammation over time. Symptoms may not appear for decades. It's difficult to get an accurate diagnosis after so much time has passed since exposure.

Screening Can Be a Valuable Tool

The US Preventative Services Task Force recommends annual screening with low-dose computed tomography (LDCT) for high-risk individuals, but there remains considerable debate because of the benefit vs risk factor. Early diagnosis leads to more effective treatment, but critics believe unnecessary CT scans also lead to false-positive results, excessive radiation exposure, lead-time bias, over management of tiny nodules, unnecessary surgeries, and poor cost management.

Researchers from the University of Michigan have developed a novel, personalized lung cancer screening tool that incorporates past asbestos exposure as a criterion to guide individuals and physicians in determining their lung cancer screening options. Adding asbestos to the lung-cancer screening tool also should help identify mesothelioma in its earliest stages when patients have more treatment options and treatments are typically more effective.

The innovative screening tool could help medical professionals fine-tune their advice to patients so that it’s based not just on a patient’s individual pulmonary cancer risk and the potential benefits of screening and its harms, but also a likely range of patient attitudes concerning problems and consequences that could arise with screening.

A patient data section within the tool includes the critical question: “Has the patient been exposed to asbestos at work?”

Based on an affirmative reply, the patient will have to discuss with his or her doctor all sources of asbestos exposure and identify the duration, intensity, and circumstances under which the exposure occurred.

Because mesothelial tumors develop within the same areas of the body as more common malignancies of the lung, the results of X-rays and CT scans may mislead specialists regarding the type of cancer the patient is suffering from. As these tests can only confirm the presence of a tumor, measure its size, and identify its precise location, more specific diagnostic procedures are required to detect mesothelioma.

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