Can My Non-Small Cell Lung Cancer Transform Into Small Cell Lung Cancer?
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Is it possible for a lung cancer subtype to change from NSCLC to SCLC?
It is generally very rare. However, if it happens, it requires a different approach to treatment.
The classification of lung cancer into subtypes is crucial for devising appropriate treatment strategies. There are two overarching categories of lung cancer, each with unique characteristics - non-small cell and small cell lung cancer. The former is categorized further into three distinct subtypes.
- Non-small cell lung cancer (NSCLC):
- Small cell lung cancer (SCLC)
Transformation of NSCLC to SCLC was first reported in 2006. Since then, transformation to SCLC has been observed mostly in cases of lung adenocarcinoma and a few in squamous cell carcinoma. It is uncommon but there are cases in which the molecular profile of a tumor changes over time, leading to a transformation of the subtype.
What causes NSCLC to turn into SCLC?
Genetic mutations can still occur even after a cancer diagnosis, as it is part of the aging process. Certain genetic changes may cause
- A switch in cancer subtype if the mutation occurs in a gene that controls cell differentiation
- Treatment resistance, meaning the treatments stopped working. This happens if the driver gene that is being targeted by the drug acquires additional mutations. This can happen with EGFR-targeted therapy and immunotherapy (using immune checkpoint inhibitor). However, it is important to note that the development of treatment resistance does not necessarily indicate a transformation from NSCLC to SCLC. A biopsy to look for signs of SCLC is needed for definitive diagnosis.
Generally, SCLC progresses more aggressively than NSCLC. This means
- The cancer will grow and spread rapidly
- The outlook of this transformation is poor
While the median overall survival of NSCLC is 27 months, this may be shortened to 8.5 months after a transformation occurs. Close monitoring and routine surveillance are the key to detect such transformation early.
Detection of NSCLC transformation
Some observations to look out for:
- A worsening of cancer symptoms
- Development of new cancer symptoms
- Development of resistance to treatments (targeted, chemo- and immunotherapy)
In order to confirm that the cancer has transformed, doctors may order tests like:
When undergoing cancer treatments, it is important to monitor any changes in symptoms. Keep an eye out for:
- Worsening cough, difficulty in breathing, any form of pain
- Recurrent infections like pneumonia or bronchitis at a higher frequency
- Further weakening (fatigue) and weight loss
Lung cancer patients must stay on top of any changes in their health. Active surveillance is important for all lung cancer patients for early detection of cancer progression and subtype transformation. It can be worrisome that transformed NSCLC has a worse outlook. But every person is different. Because of this, be open and honest when communicating with your cancer care team about your fears, concerns and expectations of your specific situation.
Key Takeaways
NSCLC and SCLC are two distinct types of lung cancer with different characteristics and treatment approaches. A transformation of NSCLC to SCLC means
- the cancer has progressed and will deteriorate rapidly
- there is a need to re-plan cancer treatments; the planned treatment regimen most probably no longer works for the transformed subtype
It is important to keep cancer under check or active surveillance.
Related: Immunohistochemistry In Subtyping Non-Small Cell Lung Cancer