Which histopathological feature best distinguishes small cell lung cancer (SCLC) from non-small cell lung cancer (NSCLC)?

Question

Accepted Answer

B. Cell size: nuclei smaller than 3 times the diameter of a red blood cell with scant cytoplasm. ## Histopathological Discrimination Between SCLC and NSCLC ### Key Morphological Criterion **Key Point:** The defining feature of SCLC is the **small cell size** — nuclei are typically **smaller than 3 times the diameter of a red blood cell** (RBC), with a **very high nuclear-to-cytoplasmic ratio** and **scant cytoplasm**. This is the gold standard for diagnosis. ### Comparison Table | Feature | SCLC | NSCLC | | --- | --- | --- | | **Nuclear size** | <3× RBC diameter | >3× RBC diameter | | **Cytoplasm** | Scant, barely visible | Abundant | | **N:C ratio** | Very high (>80%) | Lower (50–70%) | | **Chromatin pattern** | Fine, "salt-and-pepper" | Coarser | | **Nucleoli** | Inconspicuous | Prominent | | **Mitotic rate** | Very high (>10 per 10 hpf) | Variable | ### Microscopic Appearance **High-Yield:** SCLC cells appear as a **monotonous sheet of small, round-to-oval cells** with **minimal cytoplasm**, often described as resembling **lymphocytes or basophilic granules**. The nuclei are densely packed and appear to overlap. ### Why This Matters Clinically **Clinical Pearl:** This morphological distinction is not merely academic — it determines: - **Chemotherapy sensitivity:** SCLC is highly chemosensitive (initially); NSCLC is relatively resistant. - **Prognosis:** SCLC has a worse median survival (8–13 months untreated) despite better initial response to chemotherapy. - **Staging:** SCLC uses a 2-stage system (limited vs. extensive); NSCLC uses TNM staging. ### Immunohistochemical Confirmation **Key Point:** When morphology is ambiguous, IHC markers help: - **SCLC:** TTF-1+, chromogranin+, synaptophysin+, CD56+, AE1/AE3 (cytokeratin)+ - **NSCLC adenocarcinoma:** TTF-1+, mucin+, CK7+ - **NSCLC squamous:** p63+, CK5/6+, desmoglein-3+ ### Mnemonic for SCLC Morphology **Mnemonic: "SCLC = SMALL"** - **S** = Small nuclei (<3× RBC) - **M** = Minimal cytoplasm (scant) - **A** = Apoptotic bodies (high mitotic rate) - **L** = Lymphocyte-like appearance - **L** = Limited chromatin detail ("salt-and-pepper") [cite:Robbins 10e Ch 15]

Answer

A. Cell size: nuclei larger than 3 times the diameter of a red blood cell

Answer

C. Presence of mucin production and glandular differentiation

Answer

D. Keratinization and intercellular bridges on light microscopy

Which histopathological feature best distinguishes small cell lung cancer (SCLC) from non-small cell lung cancer (NSCLC)?

Explanation

Histopathological Discrimination Between SCLC and NSCLC

Key Morphological Criterion

Comparison Table

Microscopic Appearance

Why This Matters Clinically

Immunohistochemical Confirmation

Mnemonic for SCLC Morphology

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Feature	SCLC	NSCLC
Nuclear size	<3× RBC diameter	>3× RBC diameter
Cytoplasm	Scant, barely visible	Abundant
N:C ratio	Very high (>80%)	Lower (50–70%)
Chromatin pattern	Fine, "salt-and-pepper"	Coarser
Nucleoli	Inconspicuous	Prominent
Mitotic rate	Very high (>10 per 10 hpf)	Variable