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Lung tumor

Adenocarcinoma

Adenocarcinoma-classification


Reviewers: Fulvio Lonardo, M.D. (see Reviewers page)
Revised: 11 January 2013, last major update September 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

General
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● In February 2011, Travis et al. reported, on behalf of multiple agencies, a revised classification (J Thorac Oncol 2011;6:244, PDF)

Differences from 2004 WHO classification of Lung-Adenocarcinoma
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● Mixed subtype is mostly dropped (previously included 95% of all cases so not that helpful); call "mixed mucinous and non mucinous" if at least 10% of each component is present
● Concept of “predominant” growth pattern is added (predominant: largest percentage, even if <50%)
● Minimally Invasive Adenocarcinoma (MIA) type is added; predominant lepidic growth pattern; excellent prognosis if invasion of 5 mm or less
● Lepidic predominant and mucinous adenocarcinoma are added as variants; lepidic is defined as “growth restricted to neoplastic cells, along preexisting alveolar structures, lacking stroma, vascular or pleural invasion, with no papillary or micropapillary patterns, and no intra-alveolar tumor cells
● Bronchioloalveolar carcinoma (BAC) is dropped; BAC growth pattern regarded as pre-invasive lesion; entities formerly known as BAC, i.e. tumors with a prominent or exclusive lepidic growth pattern, are reclassified based on size and morphological features
● Adenocarcinoma in situ (AIS) is subdivided into nonmucinous and mucinous variants, but virtually all cases are non-mucinous, consisting of type II pneumocytes or Clara cells; considered an intermediate step between normal and invasive adenocarcinoma; has lepidic growth pattern; no papillary or micropapillary patterns, no intra-alveolar tumor cells

Bronchioloalveolar carcinoma: how to classify tumors now
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1. <=3cm, NO stromal, lymphatic, vascular or pleural invasion, no necrosis, no growth patterns other than lepidic:
● Adenocarcinoma in situ, either serous or mucinous

2. <=3cm, with <=5mm area of stromal invasion or growth pattern(s) other than lepidic:
● Minimally Invasive Adenocarcinoma (MIA)

3. >3cm OR lymphatic, vascular or pleural invasion OR necrosis OR >5mm area of stromal invasion OR growth pattern(s) other than lepidic:
● Serous: invasive adenocarcinoma, lepidic predominant or
● Mucinous: invasive mucinous adenocarcinoma

● Invasion defined as histological subtypes other than lepidic or presence of a myofibroblastic stroma associated invasive tumor
● For tumors with multiple foci, measure largest dimension on a single slide; do NOT sum invasive foci on all slides

Entities in which the term BAC was used
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● Adenocarcinoma in situ (AIS): usually nonmucinous, rarely mucinous
● Minimally invasive adenocarcinoma (MIA): usually nonmucinous, rarely mucinous
● Lepidic predominant adenocarcinoma (LPA): nonmucinous
● Adenocarcinoma, predominantly invasive, with some nonmucinous lepidic component: includes some resected tumors formerly classified as mixed subtype and some clinically advanced adenocarcinomas formerly classified as nonmucinous BAC
● Invasive mucinous adenocarcinoma: formerly mucinous BAC

Clinical features
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● Multifocal / lobal / bilateral involvement is frequent in invasive mucinous, rare in nonmucinous (AIS/MIA/LPA)

Micro description
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● Invasive mucinous: composed primarily of mucin filled columnar goblet cells
● Non mucinous tumors (AIS, MIA, LPA): composed primarily of Type II pneumocytes or Clara cells
● Note: invasive adenocarcinomas that secrete mucin but lack goblet cells or columnar cells should not be classified as mucinous adenocarcinoma, but are classified based on the predominant growth pattern adding “with mucinous features” or “with mucin production”
● Note: tumors with a lepidic growth pattern may represent metastatic mucinous tumors of pancreas, ovary, other

Staining patterns
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● Invasive mucinous: CK7 (90%), CK20 (54%), TTF1 (17%)
● Non mucinous tumors (AIS/MIA/LPA): CK7 (98%), CK20 (5%), TTF1 (67%)

End of Lung tumor > Adenocarcinoma > Adenocarcinoma-classification


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