Table 2. Diagnosis, terminology and recommendations in small specimens.

Pathologic characteristics	2004 WHO terminology	IASLC/ATS/ERS terminology
Clear morphologic features present
Presence of glands or mucin	Adenocarcinoma. Patterns are described if clearly present	Adenocarcinoma. Describe patterns if clearly present. Considerations: AIS/MIA cannot be diagnosed in small biopsies; if pure lepidic pattern/growth seen, add comment on invasive adenocarcinoma cannot be excluded nor assumed
Presence of keratinization, pearls or intercellular bridges	Squamous-cell carcinoma	Squamous-cell carcinoma
No morphologic features but distinctive positive immunostaining
TTF-1 (or napsin A)	No specific terminology. Usually diagnosed as solid adenocarcinomas	NSCLC-favor adenocarcinoma
p63 (or p40 or CK 5/6)	No specific terminology	NSCLC-favor squamous-cell carcinoma
Conflicting results of morphology and IHC (Mixed)	No clear recommendations	Individualize. Considerations: adenosquamous tumors can only be diagnosed in resection specimens with >10% of each component present; almost all TTF-1 and p63 positive are adenocarcinomas
No differentiation by morphology or IHC (both negative)	Large-cell carcinoma	NSCLC-NOS. Considerations: avoid the use of the term large-cell carcinoma in small specimens (restricted to resection specimens); this term should be used as little as possible

WHO, World Health Organization; IASLC, International Association for the Study of Lung Cancer; ATS, American Thoracic Society; ERS, European Respiratory Society; AIS, adenocarcinoma in situ; MIA, minimally invasive adenocarcinoma; NSCLC, non-small-cell lung cancer; NOS, not otherwise specified; IHC, immunohistochemistry.