Small Cell Lung Cancer

Neuroendocrine lung malignancy, paraneoplastic syndromes, limited vs. extensive-stage disease, and platinum-etoposide plus checkpoint inhibition

Key Points

• SCLC accounts for ~13–15% of all lung cancers (~30,000 cases/year in the US); it is almost exclusively caused by cigarette smoking.
• SCLC is classified as limited-stage (LS-SCLC, confined to one hemithorax) or extensive-stage (ES-SCLC, beyond one hemithorax); ~60–70% present with extensive-stage disease.
• SCLC has the highest mutation burden of any solid tumor and near-universal inactivation of TP53 and RB1.
• Paraneoplastic syndromes are common: SIADH, Cushing syndrome (ectopic ACTH), Lambert-Eaton myasthenic syndrome (LEMS), and paraneoplastic encephalitis.
• Limited-stage SCLC is treated with concurrent cisplatin/etoposide + thoracic radiation — ~20–25% are cured.
• Extensive-stage SCLC first-line standard: carboplatin + etoposide + atezolizumab or durvalumab (checkpoint inhibitor addition modestly improves OS).
• SCLC frequently responds dramatically to initial chemotherapy but almost invariably relapses within months — resistant relapse carries a very poor prognosis.

Epidemiology & Incidence

Small cell lung cancer (SCLC) is a high-grade neuroendocrine carcinoma of the lung. It represents approximately 13–15% of all lung cancers in the US (~30,000 new cases annually). Unlike non-small cell lung cancer (NSCLC), SCLC has a near-exclusive relationship with cigarette smoking: >95% of cases occur in current or former heavy smokers. The risk correlates with pack-year history; never-smokers with SCLC are exceedingly rare (<1%). The incidence of SCLC has declined in parallel with declining smoking rates in men, but has shown a relative increase in women consistent with trends in female…

Molecular Biology & Risk Factors

SCLC has a distinctive molecular profile: • TP53 inactivation: ~90% of cases; the tumor suppressor p53 is almost universally lost. • RB1 inactivation: ~90% of cases; loss of the retinoblastoma protein drives unrestricted cell cycle progression, the hallmark of SCLC's rapid proliferation. • MYCL, MYCN, MYC amplification: ~20% of SCLC; MYC-amplified SCLC is particularly aggressive. • Ultra-high tumor mutational burden (TMB): SCLC has one of the highest TMBs of all solid tumors due to tobacco carcinogen-induced G→T transversions — but this has not translated into the high immunotherapy response…

Clinical Presentation

SCLC typically presents with rapid onset of symptoms reflecting central airway involvement, bulky mediastinal adenopathy, and early distant metastases: Pulmonary/intrathoracic symptoms: • Cough (persistent, often productive or hemoptysis): Most common symptom; central tumor location causes airway irritation • Dyspnea: From bronchial obstruction, pleural effusion, or phrenic nerve involvement • Superior vena cava (SVC) syndrome: Facial/neck swelling, arm edema, headache, plethora — caused by mediastinal nodal compression of the SVC; SCLC is the most common malignant cause of SVC syndrome •…

Staging & Limited-Stage Treatment

SCLC uses the Veterans Administration Lung Study Group (VALSG) two-stage system, which is clinically practical: • Limited-stage (LS-SCLC): Disease confined to one hemithorax, including ipsilateral mediastinal and supraclavicular nodes — can be encompassed within a tolerable radiation port. ~30–40% of patients. • Extensive-stage (ES-SCLC): Beyond one hemithorax — contralateral mediastinal/supraclavicular nodes, pleural effusion, distant metastases. ~60–70% of patients. TNM staging (AJCC 8th edition) is also used, particularly for surgical candidates (very small T1 N0 SCLC — rare). Workup: CT…

Extensive-Stage Treatment

Extensive-stage SCLC (ES-SCLC) is not curable with standard therapy but is highly chemosensitive at first presentation. The first-line standard is platinum-etoposide doublet chemotherapy combined with a PD-L1 checkpoint inhibitor, continued as maintenance after the induction phase. • Atezolizumab (anti-PD-L1) + carboplatin + etoposide × 4 cycles → atezolizumab maintenance (IMpower133): mOS 12.3 vs. 10.3 months (HR 0.70) — first immunotherapy regimen to improve OS in ES-SCLC; FDA approved 2019. • Durvalumab (anti-PD-L1) + platinum-etoposide × 4 cycles → durvalumab maintenance (CASPIAN): mOS…

Relapsed / Refractory SCLC

SCLC almost universally relapses after first-line platinum-etoposide ± checkpoint inhibitor. The relapsed setting is stratified by platinum-free interval (PFI): • Platinum-sensitive relapse (PFI ≥90 days): Rechallenge with platinum-based therapy or second-line single agents. Topotecan (IV or oral) has been the FDA-approved standard since 1996. Lurbinectedin (marine-derived alkylating agent, FDA approved 2020 under accelerated approval based on a phase II basket study) yields ORR ~35% and is an alternative for sensitive or resistant relapse. Tarlatamab (DLL3 × CD3 bispecific T-cell engager,…