Small cell lung cancer (SCLC) is a highly aggressive neuroendocrine malignancy of the lung that accounts for approximately 10–15% of all lung cancers. It is strongly associated with cigarette smoking and is characterized by rapid tumour growth, early dissemination, and a high propensity for widespread metastasis at the time of diagnosis.

SCLC is highly sensitive to chemotherapy and radiotherapy during the initial stages of treatment. However, despite high initial response rates, most patients eventually experience disease recurrence, and long-term cure rates remain low. Because of its aggressive nature, treatment is usually systemic even when disease appears localized.

Unlike non-small cell lung cancer (NSCLC), SCLC is commonly staged as either limited-stage disease or extensive-stage disease, which guides treatment decisions.

Epidemiology

SCLC accounts for approximately 10–15% of all lung cancers worldwide.

Epidemiological characteristics include:

• Strong association with cigarette smoking

• Rare among never-smokers

• More common in older adults

• Slight male predominance in many populations

• Frequently presents with metastatic disease at diagnosis

Risk factors

Cigarette smoking

The most important risk factor

Risk increases with:

• Duration of smoking

• Number of cigarettes smoked

• Pack-year exposure

Passive smoking

Long-term exposure to second-hand smoke increases risk

Occupational exposures

Including:

• Asbestos

• Radon

• Arsenic

• Chromium

• Nickel

• Silica

Environmental pollution

Including:

• Indoor biomass fuel exposure

• Air pollution

• Industrial pollutants

Previous lung disease

Including:

• Chronic obstructive pulmonary disease

• Pulmonary fibrosis

• Previous pulmonary tuberculosis

Family history

A family history of lung cancer may increase susceptibility

Pathophysiology

SCLC originates from neuroendocrine cells within the bronchial epithelium.

The disease is characterized by:

• Rapid cellular proliferation

• High mitotic activity

• Early vascular invasion

• Early lymphatic spread

• High metastatic potential

Common sites of metastasis include:

• Brain

• Bone

• Liver

• Adrenal glands

• Bone marrow

SCLC frequently produces paraneoplastic syndromes due to ectopic hormone production.

Common paraneoplastic syndromes include:

• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

• Cushing syndrome

• Lambert-Eaton myasthenic syndrome

Clinical presentation

Most patients present with advanced disease because of the rapid growth and early metastatic spread of the tumour.

Clinical manifestations may arise from:

• Primary thoracic disease

• Mediastinal involvement

• Metastatic disease

• Paraneoplastic syndromes

Symptoms

Respiratory symptoms

• Persistent cough

• Haemoptysis

• Chest pain

• Dyspnoea

• Wheezing

Constitutional symptoms

• Weight loss

• Fatigue

• Loss of appetite

• General weakness

Symptoms of superior vena cava obstruction

• Facial swelling

• Neck vein distension

• Upper limb swelling

• Headache

• Dyspnoea

Symptoms of brain metastases

• Headache

• Seizures

• Altered mental status

• Focal neurological deficits

Symptoms of bone metastases

• Bone pain

• Pathological fractures

Symptoms of liver metastases

• Right upper quadrant pain

• Jaundice

• Abdominal swelling

Symptoms of paraneoplastic syndromes

• Muscle weakness

• Hyponatraemia-related symptoms

• Features of hypercortisolism

Clinical signs

General findings

• Weight loss

• Cachexia

• Poor performance status

Respiratory findings

• Reduced breath sounds

• Pleural effusion

• Wheezing

• Localized crackles

Signs of superior vena cava obstruction

• Facial oedema

• Neck vein distension

• Upper limb oedema

• Cyanosis

Neurological findings

• Focal neurological deficits

• Altered consciousness

• Cranial nerve abnormalities

Skeletal findings

• Bone tenderness

• Pathological fractures

Hepatic findings

• Hepatomegaly

• Jaundice

Differential diagnosis

• Non-small cell lung cancer

• Pulmonary tuberculosis

• Pneumonia

• Bronchiectasis

• Lung abscess

• Pulmonary fibrosis

• Metastatic lung tumours

• Mediastinal tumours

• Lymphoma

Diagnostic criteria

SCLC should be suspected in patients presenting with:

• Persistent respiratory symptoms particularly in smokers

• Haemoptysis

• Unexplained weight loss

• Superior vena cava obstruction syndrome

• Rapid progression of symptoms

• Evidence of metastatic disease

Diagnosis is confirmed by:

• Imaging findings suggestive of lung malignancy

• Histopathological confirmation from biopsy or cytology

Investigations

Laboratory investigations

Full blood count (FBC)

Used to assess:

• Anaemia

• Infection

• Baseline treatment status

Liver function tests (LFTs)

Assess:

• Hepatic function

• Liver metastases

Renal function tests

Including:

• Urea

• Creatinine

Imaging investigations

Chest X-ray (PA and lateral views)

May demonstrate:

• Lung mass

• Hilar enlargement

• Mediastinal widening

• Pleural effusion

CT scan of thorax and abdomen

Used for:

• Tumour assessment

• Staging

• Evaluation of nodal disease

• Detection of metastases

Abdominal ultrasound

Useful for evaluation of abdominal metastases

Brain CT scan or MRI

Required because of the high incidence of brain metastases

Endoscopic investigations

Bronchoscopy

Allows:

• Direct visualization of the tumour

• Tissue biopsy

• Bronchial washings and brushings

Cytological investigations

Sputum cytology

May identify malignant cells

Bronchial aspirate cytology

Useful for diagnosis in selected patients

Bone marrow examination

Bone marrow aspirate

Recommended because bone marrow involvement may occur early in the disease

Histopathology

Confirms:

• Small cell carcinoma

• Neuroendocrine differentiation

• Tumour subtype

Staging

SCLC is staged as:

Limited-stage disease

Disease confined to one hemithorax and regional lymph nodes that can be encompassed within a tolerable radiotherapy field

Extensive-stage disease

Disease extending beyond a single radiotherapy field or with distant metastatic spread

Management

Management should be undertaken by a multidisciplinary oncology team.

Treatment objectives include:

• Disease control

• Symptom relief

• Improved survival

• Preservation of quality of life

Management pathway:

1. Confirm diagnosis

2. Determine disease stage

3. Assess performance status

4. Initiate systemic therapy

5. Consider radiotherapy where indicated

6. Provide supportive and palliative care

Non-pharmacological treatment

Supportive care

Includes:

• Nutritional support

• Smoking cessation

• Pain management

• Psychosocial support

• Management of complications

Radiotherapy

Radiotherapy plays an important role in both curative-intent and palliative treatment.

Consolidation thoracic radiotherapy

Indicated for selected responders after chemotherapy.

Recommended dose:

• 50 Gy in 25 fractions over 5 weeks

Prophylactic cranial irradiation (PCI)

Indicated in patients achieving complete response after initial treatment to reduce the risk of brain metastases.

Palliative radiotherapy

Indicated for symptom relief in:

• Respiratory symptoms

• Bone metastases

• Brain metastases

• Central nervous system involvement

• Superior vena cava obstruction

Recommended dose:

• 30 Gy in 10 fractions over 2 weeks

Pharmacological treatment

First-line chemotherapy

Cisplatin and etoposide regimen

Cisplatin – 60 mg/m² – intravenous infusion over 1 hour – day 1ANDEtoposide – 100 mg/m² – intravenous infusion over 30 minutes – day 1 to day 3

Frequency:

• Every 21 days

Duration:

• 4–6 cycles

Carboplatin and etoposide regimen

Carboplatin – AUC 5 – intravenous infusion over 1 hour – day 1ANDEtoposide – 100 mg/m² – intravenous infusion over 30 minutes – day 1 to day 3

Frequency:

• Every 21 days

Duration:

• 4–6 cycles

Other active chemotherapeutic agents

Additional agents that may be used in selected cases include:

• Irinotecan

• Gemcitabine

Management according to disease stage

Limited-stage disease

Management includes:

• Platinum-based chemotherapy

• Concurrent or sequential thoracic radiotherapy

• Prophylactic cranial irradiation in complete responders

Extensive-stage disease

Management includes:

• Systemic chemotherapy

• Palliative radiotherapy as indicated

• Supportive care

Recurrent disease

Management may include:

• Second-line chemotherapy

• Palliative radiotherapy

• Symptom-directed supportive care

Referral

All patients with suspected or confirmed SCLC should be referred urgently to specialized oncology centres.

Urgent referral indications

• Haemoptysis

• Superior vena cava obstruction syndrome

• Suspected spinal cord compression

• Brain metastasis symptoms

• Respiratory compromise

• Rapidly progressive disease

Complications

Disease-related complications

• Superior vena cava obstruction

• Brain metastases

• Bone metastases

• Liver metastases

• Bone marrow infiltration

• Pleural effusion

• Respiratory failure

• Paraneoplastic syndromes

Treatment-related complications

Chemotherapy

• Myelosuppression

• Neutropenic sepsis

• Nausea and vomiting

• Nephrotoxicity

• Peripheral neuropathy

Radiotherapy

• Radiation pneumonitis

• Oesophagitis

• Fatigue

• Pulmonary fibrosis

Prognosis

SCLC is an aggressive malignancy with a generally poor prognosis.

Prognosis depends on:

• Disease stage

• Performance status

• Response to chemotherapy

• Presence of metastases

• Development of recurrent disease

Although initial response rates are high, recurrence is common and remains the leading cause of mortality.

Prevention

Tobacco control

• Smoking cessation

• Avoidance of second-hand smoke

• Public smoking prevention programmes

Occupational protection

• Minimize exposure to asbestos

• Minimize exposure to radon

• Use appropriate workplace protective measures

Environmental protection

• Reduce exposure to air pollution

• Reduce exposure to biomass fuel smoke

Early detection

• Prompt evaluation of persistent respiratory symptoms

• Early investigation of haemoptysis

• Surveillance of high-risk individuals