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ORAL 24 - CT Detected Nodules - Predicting Biological Outcome (ID 122)
- Event: WCLC 2015
- Type: Oral Session
- Track: Screening and Early Detection
- Presentations: 1
ORAL24.05 - Reclassification of Lung Cancers Detected by CT Imaging in the American College of Radiology Imaging Network National Lung Screening Trial (ID 1454)
10:45 - 12:15 | Author(s): R.D. Achcar
The National Lung Screening Trial (NLST) found a 20% reduction in lung cancer-specific mortality using low dose CT vs chest radiography for screening. The magnitude of mortality benefit has been questioned given that a higher proportion of tumors in the CT arm were diagnosed as “bronchioloalveolar cell carcinoma”. Subsequent to the initiation of the NLST, the pathological classification of lung cancer was revised to take into account the reported favorable outcome for solitary in situ nodules <3 cm. The term “bronchioloalveolar carcinoma” (BAC) was eliminated in favor of the more explicit terms adenocarcinoma in situ (AIS), microinvasive adenocarcinoma (MIA), and invasive carcinoma with various predominant histological patterns. To better assess the impact of these recent changes in the Pathological classification of lung cancer on possible over-diagnosis in the NLST, we have reviewed the histology of lung tumors detected through the ACRIN-NLST trial and reclassified them according to the most recent WHO pathology classification.
Histology was initially classified by the pathologists at sites where NLST participants were managed. Representative slides of 192 surgical resection specimens and 15 non-surgical biopsies from 207 patients were collected from 19 participating institutions. Digital images were prepared from 533 glass H&E stained slides using an Aperio digital slide imager. Digital images were examined by three pulmonary pathologists (WAF, DTM and JDH) and reclassified according to criteria and nomenclature of the recently published 2015 edition of the WHO classification.
There was 92% concordance between submitting and reference pathologists when cases were grouped into the broad categories of adenocarcinoma, squamous carcinoma, neuroendocrine and large cell lung carcinoma (LCLC). The WHO classification permitted a more detailed analysis of the tumors. Invasive adenocarcinoma was the largest tumor category comprising 61% (127) of all tumors and included 70 acinar tumors, 23 solid, 13 papillary, 8 micropapillary, 5 mixed mucinous/non-mucinous, 4 invasive mucinous, 3 lepidic and 1 adenocarcinoma that could not be further classified. There were 48 (23%) squamous tumors, 10 (5%) LCLC, 15 (7%) neuroendocrine tumors including 6 (3%) small cell lung carcinomas. Finally, one tumor had sarcomatoid histology and an additional tumor was classified at sclerosing pneumocytoma. On reclassification, only 5 of the 26 tumors originally referred to as BAC or as having BAC features by submitting pathologists met criteria for adenocarcinoma in situ or minimally invasive carcinoma. Twenty-one of these 26 tumors were reclassified as invasive adenocarcinoma, most frequently acinar pattern predominant (8 cases).
Reclassification of tumors identified through low dose CT screening in the National Lung Screening Trial permitted a detailed analysis of histological features and should permit a more nuanced assessment of biology and prognosis of this important cohort than has been available to date. Reclassification of BAC mainly as invasive adenocarcinoma conflicts with the suggestion that much of the benefit in the NLST CT screening trial was derived from surgical removal presumably non-invasive low grade tumor. *ACRIN received funding from the National Cancer Institute through the grants U01 CA079778 and U01 CA080098.
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