The Science Of Health: Why Small Cell Lung Cancers Grow Faster Than Non-Small Cell Cancers, But Are Less Common

Small cell lung cancer, also known as oat cancer, accounts for about 10 to 15 per cent of all lung cancers. Non-small cell lung cancers account for 80 to 85 per cent of lung cancers.

Lung cancer: This week, explain the difference between small cell lung cancers and non-small cell lung cancers, understand why small cell lung cancers spread faster than non-small cell lung cancers, and know why small cell lung cancers are less common than non-small cell lung cancer

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Lung cancer: Welcome back to “The Science Of Health”, ABP Live’s weekly health column. Last week, we discussed the scientific reasons behind hormonal changes exacerbating asthma symptoms in women, and ways to prevent the worsening of conditions. This week, explain the difference between small cell lung cancers and non-small cell lung cancers, understand why small cell lung cancers spread faster than non-small cell lung cancers, and know why small cell lung cancers are less common than non-small cell lung cancers, despite the former spreading faster than the latter.

Lung cancer is the leading cause of cancer-related deaths in the country, and is responsible for about 14 per cent of all cancer-related deaths in the country. Lung cancer is of two types, small cell lung cancer and non-small cell lung cancer. Small cell lung cancer cells appear smaller and flatter compared to non-small cell cancer cells under a microscope. 

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Small cell lung cancer, also known as oat cancer, accounts for about 10 to 15 per cent of all lung cancers. Small cell lung cancer cells also grow and spread faster than non-small cell lung cancer cells. In the case of small cell lung cancer, the cells have already spread beyond the lungs at the time of diagnosis of the disease. Small cell lung cancer patients respond well to radiation therapy and chemotherapy because the cancer cells spread fast. However, the chances of relapse are high. 

Non-small cell lung cancers account for 80 to 85 per cent of lung cancers. It is of three types: adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. Adenocarcinoma usually occurs in smokers or people who were smokers in the past, and manifests itself in cells that normally secrete mucus. Surprisingly, adenocarcinoma is the most common type of lung cancer observed in non-smokers. 

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According to the American Cancer Society, adenocarcinoma is likely to be detected before it has spread, is more likely to occur in younger people compared to other types of cancers, and is more common in women than in men. 

Squamous cell carcinoma begins in squamous cells of the lung airways, and usually occurs in the central part of the lungs, near the bronchus, which is the main airway. 

Large cell carcinoma is a type of non-small cell lung cancer that can occur in any part of the lungs, and is harder to treat because it grows and spreads quickly. 

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Why small cell lung cancers spread faster than non-small cell lung cancers, but are less common

Despite the fact that small cell lung cancers spread faster than non-small cell lung cancers, the former are less common than the latter. 

Since August is World Cancer Support Month, ABP Live spoke to Dr Swapnil Mehta, Full Time Consultant, Pulmonology & Sleep Medicine, at Dr. L. H. Hiranandani Hospital, Powai, Mumbai; and Dr Charu Dutt Arora, Consultant Physician and Infectious Diseases Specialist, AmeriHealth Home Healthcare, Asian Institute of Medical Sciences, Faridabad, and asked them about the scientific reasons why small cell lung cancers grow faster than non-small cell lung cancers, but are less common. 

The distinct characteristics of small cell lung cancers and non-small cell lung cancers are the main reason why non-small cell lung cancers are more prevalent, despite the fact that small cell lung cancers grow faster. 

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Explaining that non-small cell lung cancer includes various histologic subtypes, such as adenocarcinoma, squamous cell carcinoma, and large cell carcinoma, each of which originates from different lung cells, Dr Mehta said, “Small cell lung cancer is a more homogeneous group with aggressive behaviour, which is usually diagnosed and treated first. Furthermore, smoking is an important risk factor for lung cancer and non-small cell lung cancer is more closely associated with smoking compared to small cell lung cancer. Smoke accumulates carcinogens over time, resulting in genetic mutations that ultimately lead to non-small cell lung cancer.”

Smoking is a major reason behind non-small cell lung cancers being more common.

Dr Mehta explained that since the prevalence of smoking is still relatively high, especially in certain populations, this is an important contributor to the increase in non-small cell lung cancer. “Furthermore, advances in screening protocols and imaging technologies have facilitated the early detection of non-small cell lung cancer, especially when it is still localised, allowing curative therapy. On the other hand, small cell lung cancer grows rapidly and occurs more frequently in more advanced settings. This limits treatment opportunities and affects overall survival rates.”

Therefore different histological subtypes, associations with smoking, and differences in diagnostic methods contribute to the high prevalence of non-small cell lung cancer.

Explaining that the mere nature of small cell lung cancer cells is aggressive, as a result of which they proliferate extensively, Dr Arora said, “There is a neuroendocrine component in this type of cancer and is detected in later stages, which is resistant to any surgical intervention. The only therapeutic approaches are radiation therapy, chemotherapy, and immunotherapy.”

Translational research has shown that there is a possibility of the fast growth rate of small cell lung cancers being linked to a gene called PLCG2, which makes a protein that acts as a second messenger. The protein relays signals from one protein to another very quickly, Dr Arora said. “Such genes are highly expressed in stem cell-like lines and that is why the proliferation of small cells is so fast.”

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