Small-cell lung cancer

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Small-cell lung cancer is a poorly differentiated high-grade neuroendocrine cancer with near-universal disruption of TP53 and RB1. It usually arises centrally, producing cough, haemoptysis, recurrent collapse and bulky mediastinal nodes. Growth and dissemination are rapid, so constitutional symptoms, SVCO, liver or bone disease and brain metastases are frequent at diagnosis. Tissue may be fragile and crushed; specialist morphology and neuroendocrine immunohistochemistry must distinguish SCLC from other high-grade and well-differentiated tumours.

Staging is deliberately fast and decision-led. Contrast CT chest and upper abdomen establishes thoracic and common metastatic burden; brain MRI detects asymptomatic intracranial disease; PET-CT is most useful when limited-stage radical treatment is being planned or a finding needs resolution. TNM stage is recorded, but limited versus extensive stage remains clinically useful: limited disease can fit within a safe radical thoracic field, while extensive disease cannot. Bone marrow biopsy and indiscriminate tests are not routine when imaging already defines stage.

Limited-stage disease is treated with curative-intent concurrent platinum-etoposide and thoracic radiotherapy for a fit patient. Starting radiation early improves integration but requires rapid staging, planning and supportive preparation. Surgery has a rare role in very early node-negative disease confirmed through invasive nodal staging and is followed by systemic treatment. After a good response, the brain-control strategy may include prophylactic cranial irradiation or MRI surveillance after discussion of intracranial risk and cognitive effects.

Extensive-stage disease is systemic from the outset. Platinum-etoposide combined with a funded checkpoint inhibitor is a common first-line approach, followed by immunotherapy maintenance in responders, while urgent radiotherapy treats brain, airway, bone or cord complications. At relapse, treatment depends on the treatment-free interval, prior toxicity, performance and current approvals; platinum-sensitive recurrence differs from early refractory growth. Palliative care is introduced early because symptom burden and decision tempo are high even when systemic response is substantial.

Key points

SCLC is a high-grade neuroendocrine carcinoma strongly associated with smoking, rapid doubling, early nodal and blood spread and initial chemotherapy and radiation sensitivity.
Obtain adequate tissue quickly but avoid prolonged serial diagnostics; pathology should distinguish SCLC from NSCLC, carcinoid and large-cell neuroendocrine carcinoma.
First-line stage uses contrast CT chest and upper abdomen plus brain MRI, with PET-CT when it will refine a radical limited-stage field or resolve uncertainty.
Record both TNM and practical limited versus extensive stage: limited disease fits a tolerable radical thoracic radiotherapy field, whereas extensive disease has spread beyond it.
Preferred curative treatment for fit limited-stage SCLC is early concurrent platinum-etoposide chemoradiotherapy, commonly beginning thoracic radiotherapy with cycle one or two.
Extensive-stage first-line treatment commonly combines platinum-etoposide with an approved checkpoint inhibitor followed by maintenance immunotherapy under current NICE criteria.
Discuss prophylactic cranial irradiation or structured MRI surveillance after response according to stage, age, cognition, MRI findings and patient preference; do not apply it automatically.
Actively identify SIADH, ectopic ACTH, Lambert-Eaton syndrome, SVCO, thrombosis and treatment lysis because correcting complications can restore treatment fitness.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Tobacco carcinogen exposure

SCLC is strongly linked to cumulative cigarette exposure, with widespread genomic damage and only a small minority arising in never-smokers.

Neuroendocrine precursor transformation

Pulmonary neuroendocrine epithelial cells acquire near-universal TP53 and RB1 loss with additional alterations driving rapid proliferation.

Occupational and environmental co-exposure

Radon, asbestos and other lung carcinogens may add risk, although the smoking association is stronger than for most cancers.

Rare transformed disease

Some oncogene-driven adenocarcinomas transform histologically to SCLC under targeted-treatment pressure and require repeat tissue to identify the change.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Cell-cycle checkpoints are lost
Combined TP53 and RB1 dysfunction removes DNA-damage and retinoblastoma restraint, producing a very high growth fraction and early genomic instability.
2
Early lymphovascular spread
SCLC infiltrates mediastinal nodes and blood vessels quickly, making occult distant and brain metastases common even with a modest primary.
3
Neuroendocrine hormones are secreted
Ectopic vasopressin or ACTH and paraneoplastic autoantibodies cause SIADH, Cushing syndrome and Lambert-Eaton neurological disease remotely.
4
Initial sensitivity selects resistance
Rapidly cycling cells often respond dramatically to platinum and radiation, but resistant subclones frequently cause early systemic relapse.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Central thoracic mass

Cough, haemoptysis, breathlessness, lobar collapse and bulky mediastinal nodes are common because SCLC often arises near major bronchi.

Rapid systemic trajectory

Weeks of weight loss, fatigue, liver enlargement, bone pain or declining performance suggests early dissemination rather than a slowly localised tumour.

SVCO presentationRed flag

Facial and arm swelling, venous collaterals and positional head pressure from bulky mediastinal disease may require urgent stent or systemic treatment.

SIADH phenotypeRed flag

Euvolaemic hyponatraemia with concentrated urine can cause nausea, falls, confusion or seizure and needs severity-based correction.

Lambert-Eaton phenotype

Proximal leg weakness, dry mouth and reduced reflexes that facilitate after contraction supports a paraneoplastic presynaptic junction disorder.

Brain metastatic diseaseRed flag

Headache, focal deficit, seizure, gait change or cognitive decline requires urgent brain imaging and raised-pressure assessment.

Red flags requiring action

Stridor, monophonic wheeze, lobar collapse or severe haemoptysis suggests central airway involvement requiring urgent respiratory and interventional assessment.
Facial plethora, upper-limb swelling, orthopnoea or confusion suggests superior vena cava obstruction and possible cerebral venous compromise.
Seizure, focal deficit, headache with vomiting or altered consciousness indicates possible brain metastasis or severe hyponatraemia.
Marked hyponatraemia with confusion or seizure requires monitored emergency correction while SIADH and other causes are confirmed.
Proximal weakness, dry mouth and facilitated reflexes can precede cancer diagnosis through Lambert-Eaton myasthenic syndrome.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Core or bronchoscopic tissue diagnosisFirst step
Why
Confirm high-grade small-cell neuroendocrine morphology and exclude other lung and metastatic cancers.
Interpretation and limitations
Use morphology, proliferation and a focused immunopanel; repeat tissue when a crushed or scant sample cannot safely distinguish SCLC or suspected transformation.
02
First-line contrast CT chest and upper abdomenFirst line
Why
Define primary, nodal, pleural, liver and adrenal disease rapidly and identify complications.
Interpretation and limitations
Use findings to assign TNM and plan biopsy and radiotherapy; CT cannot exclude microscopic or small brain metastasis.
03
Brain MRI
Why
Detect intracranial disease before limited-stage radical treatment or when neurological symptoms occur.
Interpretation and limitations
MRI is preferred over CT for sensitivity and creates the baseline for brain treatment or surveillance decisions.
04
PET-CT in selected limited-stage planning
Why
Refine nodal and occult distant stage when the result changes radical-field or intent.
Interpretation and limitations
Inflammatory uptake requires correlation and sometimes tissue; do not delay urgent systemic treatment with low-value PET when extensive stage is already established.
05
FBC, renal, liver, LDH, sodium and glucose
Why
Assess treatment fitness, tumour burden and paraneoplastic metabolic disease.
Interpretation and limitations
Investigate hyponatraemia with paired serum and urine osmolality and urine sodium; cortisol, thyroid, medicines and volume state can mimic SIADH.
06
Pulmonary function and radiotherapy assessment
Why
Estimate safety of concurrent thoracic treatment and design a tolerable field.
Interpretation and limitations
Performance, lung reserve, oesophageal dose and tumour volume inform concurrent versus sequential treatment rather than age alone.
07
Invasive nodal staging for surgical candidate
Why
Confirm node-negative status in the rare very early tumour considered for resection.
Interpretation and limitations
Use EBUS or surgical staging as appropriate because occult nodal disease usually redirects treatment away from surgery.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Large-cell neuroendocrine carcinoma

High-grade neuroendocrine morphology overlaps, but cell size, architecture, necrosis and immunophenotype require specialist pathology and can alter evidence-based treatment.

Non-small-cell lung cancer

Poorly differentiated squamous or adenocarcinoma can mimic SCLC on small crushed samples; adequate tissue and immunohistochemistry prevent misclassification.

Pulmonary carcinoid

Well-differentiated neuroendocrine tumours have lower proliferation, different morphology and a more indolent surgical and systemic pathway.

Extrapulmonary small-cell cancer

Small-cell morphology can arise in bladder, prostate, cervix and other sites, requiring imaging and pathology correlation to define origin.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Stage quicklyAnswer limited versus extensive diseaseFirst stepPathology confirms or strongly supports SCLC.

1Obtain contrast CT and brain MRI promptly, adding PET-CT when it can refine a planned radical field or clarify one decisive site.
2Record TNM and whether all known disease fits a tolerable thoracic radiotherapy volume and assess performance, lung, renal, hearing and paraneoplastic complications.
3Discuss at the thoracic MDT without allowing avoidable serial tests to postpone a time-sensitive first treatment cycle.

02Limited stageDeliver early concurrent chemoradiotherapyDisease is confined to a radical thoracic field and the patient can tolerate combined treatment.

1Start platinum-etoposide and plan thoracic radiotherapy to begin early, commonly with cycle one or two, using the current radical fractionation protocol.
2Use sequential chemoradiotherapy when physiological reserve or treatment volume makes concurrence unsafe, and reserve surgery for rigorously staged very early node-negative disease.
3After response, discuss prophylactic cranial irradiation versus MRI surveillance and establish thoracic, neurological and treatment-toxicity follow-up.

03Extensive stageCombine systemic therapy and symptom controlDisease extends beyond a radical thoracic field or distant metastasis is established.

1Treat urgent brain, cord, airway, SVCO, bone, sodium and thrombotic complications and assess performance after reversible problems improve.
2Offer a current NICE-approved platinum-etoposide and checkpoint-inhibitor regimen when fit, followed by protocol maintenance, or cytotoxic or supportive alternatives when immune treatment is unsuitable.
3Use palliative radiotherapy for focal symptoms and integrate palliative care, nutrition and advance planning from diagnosis while reassessing response early.

04RelapseUse treatment-free interval and fitnessSCLC progresses after initial platinum-based treatment.

1Confirm clinical and imaging relapse and address brain or other emergency sites, distinguishing treatment toxicity and a second lung cancer when the pattern is atypical.
2Classify platinum sensitivity from the treatment-free interval and select re-challenge or another funded systemic option based on organ function and prior toxicity.
3Stop ineffective treatment promptly and prioritise breathlessness, pain, neurological and family support when expected systemic benefit is small.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Forms the systemic backbone for limited-stage chemoradiotherapy and extensive-stage first-line treatment.

Platinum with etoposide

A common 21-day specialist regimen gives cisplatin 75 mg/m² intravenously on day 1 with etoposide 100 mg/m² intravenously on days 1 to 3 for four cycles, with carboplatin substituted by protocol when renal, hearing or fitness factors require.

Use the exact NHS protocol and adjust for kidney, hearing, neuropathy and marrow reserve; prevent emesis and monitor febrile neutropenia, thrombosis, electrolyte wasting and tumour lysis.

Adds checkpoint inhibition to first-line extensive-stage SCLC and continues immune maintenance in suitable patients.

Atezolizumab with extensive-stage chemotherapy

Give atezolizumab 1,200 mg intravenously every 3 weeks with carboplatin and etoposide for four cycles, then continue 1,200 mg every 3 weeks as maintenance under the licensed and current NICE-funded regimen.

Screen autoimmune, transplant, infection and organ context and educate about delayed immune lung, bowel, liver, endocrine, cardiac, renal, skin and neurological toxicity; hold and treat according to grade.

Offers disease control after relapse when expected benefit remains meaningful and the patient is fit enough for toxicity.

Second-line systemic treatment

Use the currently funded specialist regimen selected from platinum sensitivity, previous agents, performance and organ function, with dose and cycle defined by the live SCLC protocol.

Myelosuppression and infection can be substantial in a pretreated patient; establish the response endpoint and stop early for refractory progression or unacceptable harm.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Brain metastasis

Early haematogenous spread makes intracranial disease common, causing seizure, focal deficit, cognitive change and raised pressure that influences radiotherapy strategy.

SIADH and sodium toxicity

Ectopic vasopressin causes water retention and hyponatraemia, producing confusion, falls, seizure and treatment delays if corrected unsafely.

Lambert-Eaton syndrome

Antibodies to presynaptic calcium channels cause leg-predominant weakness, autonomic symptoms and reduced reflexes that briefly facilitate after exercise.

Rapid refractory relapse

Platinum-sensitive disease can later recur with resistant disseminated tumour, worsening performance and narrowing benefit from subsequent systemic treatment.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Before each cycle, review performance, symptoms, FBC, renal, liver, sodium, magnesium, infection, hearing and neuropathy and correct paraneoplastic or treatment disturbance.
During concurrent thoracic radiotherapy, monitor swallowing, hydration, weight, cough, oxygenation and marrow toxicity and treat oesophagitis and pneumonitis promptly.
During checkpoint treatment, screen every organ system at each contact and after treatment ends, with rapid acute-oncology access for new inflammatory symptoms.
Assess response after the protocol-defined early cycles because rapid progression during treatment changes goals and prevents futile toxicity.
After limited-stage response, monitor brain according to the agreed PCI or MRI strategy and investigate symptoms outside scheduled imaging.
At relapse, document treatment-free interval, prior maximum toxicity, performance and expected benefit and involve palliative care before the next-line decision.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Fast diagnosis prevents lost time

SCLC can progress visibly during a prolonged staging sequence, so each test should answer a decision about radical field, brain or systemic treatment.

Limited stage is a radiation concept

It means known disease can fit a safe radical thoracic field, not simply that the primary appears small on one CT slice.

Hyponatraemia is not automatically SIADH

Adrenal deficiency, diuretics, renal failure and low solute intake can mimic the pattern and change treatment.

PCI is a preference-sensitive decision

Intracranial-risk reduction must be balanced with cognition, age, MRI access, stage and the patient's view of surveillance and toxicity.

Initial response can be deceptive

A dramatic early shrinkage does not guarantee cure because resistant subclones and occult dissemination make relapse common.

11Common pitfallsFrequent interpretation and management errors.

01
Allowing extensive serial investigation to delay time-sensitive treatment after adequate tissue and core staging.
02
Using limited stage as a synonym for any non-metastatic TNM stage without radiotherapy-volume assessment.
03
Calling hyponatraemia SIADH without serum and urine assessment and cortisol or medicine review.
04
Giving sequential treatment by default to a fit limited-stage patient who could tolerate early concurrent chemoradiotherapy.
05
Offering prophylactic cranial irradiation automatically without discussing MRI, cognition, age and preference.
06
Missing Lambert-Eaton syndrome or ectopic ACTH as treatable paraneoplastic causes of functional decline.
07
Continuing toxic relapse treatment without a predefined response and stopping threshold.