What Is Small Cell Lung Cancer?

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Small cell lung cancer (SCLC) accounts for approximately 15% of all lung cancers. It can cause symptoms ranging from fatigue to coughing up blood and is more aggressive than the more common non-small cell lung cancer (NSCLC). Smoking is the leading cause of SCLC, and a biopsy is needed to confirm a diagnosis. While it may respond to radiation and chemotherapy initially, SCLC can spread quickly, often making surgery or a definitive cure less viable.

Small Cell Lung Cancer Symptoms

Early on, this type of cancer doesn't usually cause any noticeable problems. But once symptoms begin, they can worsen rapidly within a few weeks.

The first symptoms of small cell lung cancer might result from lung impairment, like shortness of breath. But early symptoms of SCLC can be systemic (involving overall metabolism or body function), like weight loss.

Effects of SCLC can include:

As the tumor grows, it can invade structures near the lungs, like the chest, esophagus, and, throat, with corresponding symptoms.

Signs of Metastasis

If SCLC metastasizes (spreads) to other areas of the body, it's more likely to have systemic manifestations than when it's confined to the lungs. Metastatic SCLC can also cause problems associated with its destination location(s) in the body—sometimes without causing lung-associated symptoms at all.

Effects of metastatic SCLC can include:

Paraneoplastic Effects

SCLC can also cause paraneoplastic syndromes. These conditions occur when the cancer cells produce hormones that travel through the bloodstream and stimulate other organs or cells, typically in a harmful way.

While rare, these paraneoplastic effects are more common with SCLC than with other types of lung cancer, and they can be the first noticeable signs of the condition.

Paraneoplastic effects of SCLC can include:

  • Paraneoplastic cerebellar degeneration: Loss of coordination, erratic eye movements, and trouble controlling the voice
  • Lambert-Eaton myasthenic syndrome: Arm weakness and fatigue, vision changes, and difficulty swallowing
  • Polyneuropathy: Decreased sensation and/or muscle weakness throughout the body
  • Syndrome of inappropriate antidiuretic hormone secretion (SIADH): Weakness, fatigue, and a low sodium level in the blood
  • Paraneoplastic limbic encephalitis, which causes personality changes and memory deficits

Cause

SCLC is strongly linked to smoking, although it's also associated with other risk factors such as exposure to radon and asbestos. The incidence of SCLC has been declining in the United States, and decreased smoking rates have been considered a possible explanation why.

In general, SCLC usually begins in the large bronchi (airways) of the lungs. This type of lung cancer starts to develop when a mutation (an alteration in the genes) causes lung cells to behave in an abnormal and aggressive manner.

It's rare for someone who has never smoked to develop SCLC, so it is believed that the genetic mutations occur as a result of DNA damage caused by the toxins in cigarette smoke.

The mutations that lead to this type of cancer have been detected in the bronchial epithelium (lining) of people who have SCLC. The genetic changes cause problems that include:

  • Diminished immune function
  • Proliferation of cancer cell growth
  • PredispositIon for the cancer cells to spread to other regions of the body

Genetics

Genes associated with cancer include oncogenes and tumor suppressor genes.

Oncogenes are genes that start off healthy, but can lead to cancer when they are altered. Tumor suppressor genes are healthy genes that prevent cancer, but cease to work properly when altered by mutations.

Changes in these two types of genes are more substantial in SCLC than other types of lung cancer, and people with this cancer may have more than one type of gene mutation.

Examples of gene mutations associated with SCLC include tumor suppressor genes RB1 and TP53.

Diagnosis

Diagnosis of SCLC involves a number of approaches, including non-invasive imaging tests, bronchoscopy, and biopsy.

Some distinctive characteristics of SCLC can be defined with imaging tests like chest X-ray, computerized tomography (CT), magnetic resonance imaging (MRI), ultrasound, and positron emission tomography (PET scan). But these characteristics are not reliable enough to definitively distinguish SCLC from other types of lung cancer—or even from cancer that metastasized to the lungs from elsewhere in the body.

Often, imaging tests of other areas of the body besides the lungs are also needed to determine whether there has been metastasis of SCLC.

Biopsy

The most definitive way to verify that cancer is NCLC is with a lung biopsy sample obtained using a bronchoscope, needle, or surgery. During a bronchoscopy procedure, a flexible camera-equipped device is inserted into the nose or mouth and advanced down the throat into the bronchi in the lungs.

Using a bronchoscope, your doctor will look inside your airways and take a small sample of the tumor so it can be closely analyzed.

If the tumor cannot be biopsied using bronchoscopy (due to it being in an inaccessible location, for example), your doctor may obtain a biopsy sample with a needle inserted through the chest wall or with a more extensive surgical procedure. These invasive techniques are usually guided with imaging so the correct area can be identified.

Once a sample of the tissue is obtained, the type of cancer is diagnosed by inspection of its microscopic appearance. SCLC has a distinctive appearance, with small, relatively irregular appearing lung cells that are not lined up the way healthy lung cells are.

Staging

Traditionally, SCLC has been classified based on the Veterans Administration Lung Study Group (VALG) staging system as limited-SCC or extensive-stage SCLC.

Approximately 60% to 70% of people with SCLC already have extensive-stage disease at the time of diagnosis.

Additionally, SCLC is also classified according to the staging system used for NSCLC, which is known as the Tumor Node Metastasis (TNM) staging system.

This uses a classification structure based on the size of the tumor, the extent of lymph node involvement, and the extent of metastasis.

TNM staging is more descriptive. It uses numerical values ranging from 0 (mildest) through 4 (most severe) for each of the three factors, and subcategories indicated by letters as well.

Treatment

The treatment for SCLC includes a combination of chemotherapy, radiation therapy, and surgery. If you have this type of cancer, your treatment plan will be tailored based on the severity of your tumor, as well as your overall health, including your ability to withstand and readiness for treatment.

Treatment for SCLC can prolong survival, but it's not usually effective for curing the disease. Often, SCLC recurs after initial treatment and can become resistant to subsequent chemotherapy.

Chemotherapy

Chemotherapy is among the treatments used for SCLC, especially when lymph nodes or metastasis are involved. This approach uses powerful medication to destroy cancer cells. However, chemotherapy can be intense and may cause side effects such as hair loss and nausea.

A number of chemotherapeutic drugs are approved for treating SCLC, including Mustargen (mechlorethamine hydrochloride) and methotrexate.

Immunotherapy

Immunotherapy is a type of chemotherapy used to help modify the body's own immune system to fight disease. Unlike traditional types of chemotherapy, immunotherapy doesn't usually cause extensive systemic side effects, and it is more specifically directed to treating a certain type of cancer.

Tecentriq (atezolizumab), Opdivo (nivolumab), and Keytruda (pembrolizumab) are among the types of immunotherapy used to treat SCLC. Sometimes immunotherapy is used in combination with other types of chemotherapy, especially for recurrent cancer.

Radiation Therapy

For both limited and extensive stage cancers, radiation therapy is often used along with chemotherapy and/or surgery. Radiation therapy uses powerful X-rays to destroy cancer cells, and it can prolong survival.

It can cause side effects, however, including a weakened immune system and fatigue. It also raises the risk of another cancer developing sometime in the future.

Prophylactic cranial irradiation (PCI)—preventative radiation therapy to the brain—is sometimes recommended to lower the risk of brain metastasis, a very common site of cancer recurrence. Side effects can include cognitive changes, such as decreased memory and concentration.

Surgery

Surgery is not a common approach in the management of SCLC because this type of cancer is often metastatic at the time of diagnosis. However, surgery is occasionally considered for very early limited-stage cancers when a small isolated nodule is present in the lung.

Radiation may be considered before surgery to shrink the tumor and after surgery to prevent a recurrence. Adjuvant chemotherapy (chemotherapy after surgery) is usually recommended if surgery is done for small cell lung cancer.

Surgery might be recommended even in advanced disease when it can help reduce your symptoms and improve your quality of life, such as by removing a metastasis that is blocking the intestine.

Palliative Therapy

In addition to treatment for your SCLC, you may also need palliative care—treatment to alleviate your symptoms.

For example, you might need medication to reduce nausea, a common side effect of chemotherapy. You may also need pain medication if you have bone metastasis.

Palliative therapy can also involve interventions such as oxygen supplementation if you are having a hard time breathing. And if you have anemia (low red blood cells) due to a problem like coughing up blood, you might need to have a blood transfusion.

If you have any bothersome symptoms of your condition, do not hesitate to ask for treatment, as palliative therapy can improve your quality of life at any stage of your cancer care. Your palliative cancer treatment may change throughout the duration of your disease.

Prognosis

Generally, the smaller in size and the less widespread SCLC is, the better the anticipated survival. Older age, lower performance status, and paraneoplastic effects are also associated with a worse overall prognosis.

Immunohistochemistry is a technique in which biochemical markers are identified by chemically treating biopsy samples. Some markers are associated with favorable or unfavorable prognosis or anticipated response to treatment. However, these approaches are still in development.

A Word From Verywell

Finding out that you have SCLC can be stunning, especially because this type of cancer is often recognized when it's already at a fairly advanced stage. Since SCLC might not respond well to standard treatments, you may want to consider talking to your doctor about participating in a clinical trial. You could also find it helpful to connect with a support group. And don't hesitate to reach out for help from your medical team and your own family or friends as you embark on your treatment plan.

Lung Cancer Doctor Discussion Guide

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