Differences between Lung Cancer and Mesothelioma

Lungs are very important organs in the human body. They oxygenate the blood, so the other organs can obtain the oxygen that they need to work properly. They also get rid of carbon dioxide, which might be toxic in high levels for some cells of the human body.

The air enters the lungs through the trachea and bronchi. So, anything that affects the lungs or the linings around them will affect this process. Fortunately, benign respiratory diseases are more common, including the COPDs (chronic obstructive pulmonary disease) and asthma (235 million people around the world). But, certain malignant diseases, such as lung cancer and pleural mesothelioma are each year more prevalent and have a fairly high mortality rate.

Lung cancer is defined by The American Cancer Society as the presence of carcinogenic cells in the lung tissues (parenchyma). There are 2 main types of lung cancer, including the small cell lung cancer and non-small cell lung cancer (85 to 90% of all lung cancers). This classification is histological, which means that it is based on how the carcinogenic cells look under the microscope.

Likewise, there are some subtypes of non-small cell lung cancer, the Adenocarcinoma, the Squamous cell (epidermoid) carcinoma, the Large cell (undifferentiated) carcinoma, adenosquamous carcinoma and sarcomatoid carcinoma.

On the other hand, the pleural mesothelioma is defined by Frank E. Mott as a malignant tumor which develops in the pleura as a consequence of the chronic exposure to asbestos. Mesotheloma also has different subtypes. However, it is very important to highlight that this cancer can be anatomically classified according to the place of the body where it is located (such as pleural, peritoneal, testicular and pericardial) and histologically classified according to the cell types that it has. These histological subtypes are Epithelioid, Sarcomatoid and Biphasic.

Lung cancer and mesothelioma are very similar diseases that can be easily confused in the daily clinical practice, even by experienced doctors. These types of cancer are so closely related that experts say that when a patient has been diagnosed with one of them, the other one must be discarded to avoid further complications or the ineffectiveness of the treatment. Likewise, the experts always advise their patients, who have been diagnosed with lung cancer, about the chances of developing a mesothelioma later in their lives.

How can the doctors differentiate lung cancer and mesothelioma?

Although lung cancer and pleural mesothelioma are so similar, they have some differences that can allow the specialists to determine which of them the patient has and to determine the best way to treat him/her.

Causes

One of the main reasons why lung cancer and mesothelioma are so similar is the fact that both of them can be caused by a chronic exposure to asbestos. However, lung cancer also has the important antecedent of smoking, either by chronic exposure to tobacco or cigarettes.

Certain studies have corroborated the fact that patients who smoke and has a history of asbestos exposure have an increased risk of developing lung cancer, which is fifty times more than people who does not have that background. On the other hand, some researches have concluded that smoking does not increase the risk of developing a pleural mesothelioma.

Another important difference between these risk factors is that lung cancer risk decreases when a person quits smoking while the risk of developing a pleural mesothelioma increases with age even when the asbestos exposure has ceased. This is because the body cannot eliminate the asbestos fibers which are trapped in the lung tissues.

Pathophysiology

Lung cancer and pleural mesothelioma have their natural history in common. It takes decades until they develop to a size large enough to cause symptoms (the latency period usually lasts between 15 and 40 years), but once they appear, the disease spreads very quickly to distant organs. This characteristic can cause confusion in many doctors to establish a diagnosis.

Symptoms

This is a characteristic that can cause a lot of confusion when differentiating these diseases because they produce very similar symptoms. As lung cancer and mesothelioma affect the respiratory system, they can cause chest pain, breathing difficulty (dyspnoea), chronic coughing, chronic fatigue, pleural effusion and unintentional weight loss. In both diseases, these symptoms tend to arise in advanced stages.

Prevalence

One difference between lung cancer and mesothelioma is their frequency. For example, more than 220,000 Americans are diagnosed with lung cancer every year, while only 3,000 Americans are diagnosed with a pleural mesothelioma every year.

Survival

It is very important to say that both diseases have similar rates of death, being the 5-year survival rate of lung cancer nearly 18 percent and 5-year survival rate of pleural mesothelioma less than 10 percent.

Location

Another important difference between lung cancer and mesothelioma is the specific structure that they affect. For example, lung cancer affects the pulmonary parenchyma while pleural mesothelioma affects the serous membrane lining the lungs (pleura). This is the reason why pleural mesothelioma is not included among the types of lung cancer.

Diagnosis

To diagnose these diseases, the doctors can use the same tools, but some of them can help to differentiate the lung cancer from the pleural mesothelioma. For example, a biopsy with a histologic study.

The first image test that doctors usually ask for is the X-ray. It usually allows the doctor to detect a tumor growth in the lungs area. Although with this image test it is very difficult to determine if the abnormal tissue is in the lungs or the pleura, there is a sign that can help to differentiate these diseases. Patients with pleural mesothelioma usually have pleural thickening, which can be evidenced in the image tests as a scarring of the pleura, while patients with lung cancer usually do not show this finding (unless the tumor has spread to the pleura).

This is why doctors also ask for a CT, a PET-Scan (positron emission tomography) or MRI (Magnetic Resonance Imaging) which are more advanced imaging tests that can provide more detailed information about the specific structure where the tumor is located.

The biopsy is an excellent option to differentiate lung cancer from pleural mesothelioma. The doctor can obtain a sample of cancerous tissue through different methods (a fine needle puncture or a minor surgery). That sample will be examined by a qualified pathologist to determine if the patient has a lung cancer or a pleural mesothelioma.

As differentiating these diseases can be very difficult, a second pathologist can be asked to evaluate the sample. This can be explained because, under the microscope, the pleural mesothelioma can look like an adenocarcinoma (which is considered the most common type of non-small cell lung cancer) or a sarcoma (a type of soft tissue cancer).

There are other options available to differentiate a lung cancer from a pleural mesothelioma. These options include a sputum cytology test and a bronchoscopy. The sputum cytology test is non-invasive, but it has a lot of false negatives and it is not useful to diagnose a pleural mesothelioma. On the other hand, the bronchoscopy allows inserting a specialized tube with a tiny camera through the patient’s throat to the lungs, so the doctor can see the abnormal growths in the tissues and obtain a sample.

Lung cancer has certain biomarkers like the epidermal growth factor receptor (EGFR) and isocitrate dehydrogenase (IDH1). Likewise, they have detected some genetic mutations to which it is associated with, such as mutations in the gene ALK, ROS1 gene, RET gene and BRAF gene. All this biomarkers and mutations can be detected through a blood and DNA test.

On the other hand, pleural mesothelioma has been associated with certain biomarkers like mesothelin-related peptide (SMRP) and the protein called megakaryocyte potentiation factor (MPF). Likewise, the specialists have developed a test called SOMAmer, which can be used to detect more than 1,000 proteins in blood serum that can be linked to the pleural mesothelioma.

All these biomarkers tests are still under study and only a few of them have been approved by the FDA (Food and Drugs Administration), but they seem to be excellent options to make more cautious diagnosis and differentiate these diseases.

Staging

The staging of lung cancer and pleural mesothelioma is also very similar. The stages 1 and 2 refer to a localized tumor, stage 3 refers to a locally advanced tumor (it has spread to nearby organs or lymph nodes), finally, stage 4 refers to the spread of the tumor to both lungs or other organs (what is more common in lung cancer than pleural mesothelioma).

Treatment

The bases of the treatment of these diseases are the same, multimodal therapies which include the surgery, chemotherapy and radiation. However, the plans of treatment are established in different ways according to the type of tumor and the patient’s characteristics to obtain the best results.

For example, lung cancer is easy to treat with surgery because it produces well-defined masses that the surgeon can identify, which makes it easier to remove by surgery and treat with localized chemotherapy and radiation. However, the pleural mesothelioma is more difficult to identify because it appears as a thin tumor over the healthy tissue (in many cases, there are no well-defined limits between healthy and cancerous tissue), so it is very difficult to remove completely with surgery or localized chemotherapy and radiation.

It is important to say that even when radiotherapy is more recommendable for lung cancer, using this kind of treatment is very difficult in both cases due to the proximity and close relation between the lungs and other vital organs (such as the heart, the liver and the spinal cord). This treatment is more palliative (pain relieving) than curative.

The type of surgery used for treating each disease is also different. Surgeries performed to treat lung cancer usually consist of removing a portion or a lobe of the affected lung and, in some cases, the entire lung, while surgeries performed to treat pleural mesothelioma consist of removing the pleural lining and, only if it is necessary, a portion of the lung under the affected area.

Likewise, some chemotherapy agents work for lung cancer but not for pleural mesothelioma. For example, cisplatin and pemetrexed can be included among the most recommendable chemotherapy agents for treating a pleural mesothelioma, while docetaxel, vinorelbine and paclitaxel are the most recommendable agents in lung cancer treatment.

At this point, it is very important to highlight that the photodynamic therapy can also be used in both diseases, but the experts widely recommend this therapy for lung cancer while its results in pleural mesothelioma are still experimental.

It is important to remember that only a qualified and experienced doctor can determine the plan of treatment for each patient because it is always based on the patient’s particular characteristics and his/her general health condition, the subtype and stage of cancer, among others.

In conclusion, differentiating lung cancer and pleural mesothelioma can be very hard even for a qualified and experienced doctor. So, it is not weird that a medical team would be established for diagnosing and treating each patient.

This is important because it can help to avoid making mistakes by thinking about other similar and more common diseases in the first place (such as pneumonia, asthma, COPD, heart failure, among others), which can delay the diagnosis and worsen the patient’s prognosis.

So, under the suspicion of having a lung cancer or a malignant mesothelioma, the experts recommend looking for a recognized cancer center with the experience that is necessary to accurately diagnose or discard these diseases.