Mesothelioma

Malignant mesothelioma is a rare, highly aggressive cancer that arises in the mesothelium, the thin layer of specialized tissue that lines the chest cavity, abdominal cavity and other internal organs. By far the most common site is the pleura (the lining surrounding the lungs), which accounts for more than 90% of cases in men. Peritoneal mesothelioma (affecting the abdominal lining) is much less frequent and is typically linked to exceptionally heavy asbestos exposure.

The overwhelming cause responsible for roughly 90% of pleural cases in men is prolonged inhalation of asbestos fibers. Asbestos is a group of naturally occurring silicate minerals once prized for their strength, heat resistance, and insulating properties. Of the various types, the amphibole forms (especially crocidolite or “blue asbestos” and amosite or “brown asbestos”) are the most carcinogenic. These minerals break into tiny, sharp, needle-like fibers that are easily airborne.

What makes certain asbestos fibers so dangerous is their extreme biopersistence: the body’s normal clearance mechanisms (mucus, coughing, macrophages) cannot dissolve or remove them effectively. Once lodged deep in the lung tissue or pleura, the fibers remain for decades, causing persistent inflammation, scarring, and cumulative genetic damage to mesothelial cells. Over time, this chronic irritation and DNA injury disrupt normal cell-cycle control, eventually triggering malignant transformation and tumor growth.

A hallmark of mesothelioma is its extraordinarily long latency period typically 20-50 years from first exposure to diagnosis. This explains why the peak incidence in many countries is occurring now, decades after the heaviest industrial use of asbestos (1940s–1970s). Patients are often diagnosed long after retirement and far removed from the original source of contamination.

Although the classic high-risk occupations were mining, milling, asbestos product manufacturing, and shipyard work, the patient profile has evolved. Today, many cases occur in tradespeople (carpenters, plumbers, electricians) who disturb asbestos-containing materials during renovation or demolition of older buildings or appliances like old storage heaters with asbestos. Environmental and bystander exposures are also increasingly recognized:

- People living near natural asbestos deposits can inhale fibers from contaminated soil or dust.
- “Take-home” exposure occurs when workers unwittingly carry fibers home on clothing, hair, or shoes, leading to cases in spouses and children who never entered a workplace.
- Even brief, intense DIY or “handyman” encounters with asbestos during home repairs have caused disease.

Beyond asbestos, the zeolite mineral erionite found in certain volcanic regions (most notoriously in parts of Cappadocia, Turkey) has very similar fibrous structure and biopersistence and has caused devastating mesothelioma clusters in villages built with erionite-containing stone.

Symptoms are insidious and non-specific: progressive shortness of breath, chest pain, pleural effusion (fluid around the lung), unexplained weight loss, fatigue, and night sweats. Because these signs usually appear only after the cancer is advanced, and because mesothelioma can mimic adenocarcinoma or benign inflammatory conditions, definitive diagnosis requires biopsy with special immunohistochemical staining.

Histologically, mesothelioma is classified into three main subtypes:
- Epithelioid (most common, somewhat better prognosis)
- Sarcomatoid (more aggressive, spindle-cell appearance)
- Biphasic/ mixed

Regardless of subtype, overall prognosis remains poor, with median survival around 12–18 months after diagnosis. Younger age, early stage, and epithelioid histology are the main favorable factors; multimodal treatment (surgery, chemotherapy, occasionally radiotherapy) can extend survival in selected patients, but cure is rare.

Mesothelioma stands as one of the clearest examples of a completely preventable man-made cancer. No safe threshold of asbestos exposure has been established, even low or intermittent exposure can, in rare cases, trigger the disease decades later. The thousands of new cases diagnosed each year are essentially a delayed legacy of past industrial practices. Rigorous control measures during removal or disturbance of asbestos-containing materials, along with continued banning of asbestos worldwide, remain the only effective way to eliminate this disease.