Table 3. Significant differences in the IASLC/ATS/ERS-2011 classification over the WHO-2004 classification.
| Change | Description |
|---|---|
| Guidance provided for classification as per nature of pathologial specimen (resection specimens versus biopsy/cytology specimens) | Since 70% of lung cancer is unresectable at presentation, biopsy/cytology plays an important role in diagnosis and treatment guidance. The IASLC/ATS/ERS classification has provided classification guidelines for small biopsy/cytology samples, in addition to the classification for resection specimens |
| Recommendations on the use of special stains, immunohistochemistry and molecular testing | Given the paramount importance of classification of NSCLC into ADC and SqCC, recommendations are made so that in addition to routine haematoxyllin-eosin stains, optimal use of additional stains such as mucin, p63 and TTF-1 be done. Further, EGFR mutation testing too has been recommended for identifying eligibility for treatment with EGFR-TKIs |
| The term BAC is abandoned | The former term ‘BAC’ can now be represented by five separate nomenclatures in the IASLC/ATS/ERS classification |
| New concepts of AIS and MIA | For use in resected specimens, new terminologies have been provided. Small peripheral adenocarcinomas with pure lepidic growth are classified as AIS. Small peripheral adenocarcinomas (≤3 cm) with predominantly lepidic growth with invasion of ≤5 mm is classified as MIA. AIS and MIA are recognized to have 100% or near 100% dispeace specific survival after complete resection |
| Recognition of new histological subtype: ‘micropapillary’ | Recognized to have a worse prognostic outcome, the micropapillary type has been added as a new sub-type of ADC |
| Omission of ‘mixed subtype’ variant, and importance placed upon predomiant histological pattern of invasive ADC for classification | Since >90% of all lung adenocarcinomas would fall into the ‘mixed sub-type’ as per the WHO 2004 classification, invasive adenocarcinomas are now classified upon their predominate pattern after comprehensive subtyping into either of lepidic, acinar, papillary, solid or micropapillary predominant subtypes. |
| Reclassification of former terminologies of mucinous cystadenocarcinoma, colloid ADC, fetal ADC, signet ring ADC and enteric ADC | Mucinous cystadenocarcinoma is now classified as ‘invasive adenocarcinoma with enteric features’. The prior terminologies ‘colloid adenocarcinoma and fetal carcinoma’ are now renamed as ‘invasive adenocarcinoma with colloid features’, and ‘invasive adenocarcinoma with fetal pattern’, respectively. The prior terminologies of signet ring and clear cell carcinoma are now no more regarded as separate patterns. Instead, they are classified as ‘adenocarcinoma with (describe patterns present) and signet ring features’, and ‘adenocarcinoma with (describe patterns present) and clear cell features’, respectively |
ADC, adenocarcinoma; NSCLC, non-small cell lung carcinoma; SqCC, squamous cell carcinoma; TTF-1, thyroid transcription factor-1; EGFR, epidermal growth factor receptor; TKI, tyrosine kinase inhibitor; BAC, bronchioloalveolar carcinoma; MIA, minimally invasive adenocarcinoma; AIS, adenocarcinoma in situ; WHO, World Health Organization; IASLC, International Association for the Study of Lung Cancer; ATS, American Thoracic Society; ERS, European Respiratory Society.