Lung adenocarcinoma

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Author: Mikael Häggström [notes 1]


Microscopic examination


  • An adenocarcinoma in situ is defined as a tumour of ≤ 3 cm with pure lepidic pattern but no lymphatic, vascular or pleural invasion and no tumor necrosis.[1]
  • Minimally invasive adenocarcinoma: a small (≤3 cm), solitary tumour with predominant alveolar epithelial appearance (lepidic growth), as in situ adenocarcinoma of the lung, with a zone of focal invasion of the stroma with a size inferior to 5 mm.[1] It has no lymphatic, vascular or pleural invasion and no tumor necrosis.
  • Invasive adenocarcinoma: Tumor of larger size or focus of invasion, or with lymphatic, vascular, pleural invasion or tumor necrosis.

Predominant pattern

For invasive adenocarcinomas, generally specify the pattern (mainly lepidic, acinar, papillary, micropapillary, solid predominant or "predominant subtype cannot be determined).

Degree of differentiation

Lung adenocarcinomas may be classified as follows:[2]

Well differentiated Solid pattern< 90% and mild/moderate atypia
Moderately differentiated
  • Solid pattern ≥ 90% and mild/moderate atypia
  • Solid pattern< 90% and severe atypia
Poorly differentiated Solid pattern ≥ 90% and severe atypia



Tumor size

If the tumor has both lepidic and invasive components, specify the maximum dimension of each.

Growth into adjacent structures

Notable adjacent structures possibly involved are:[3]

  • Parietal pleura
  • Main bronchus
  • Hilar soft tissues
  • Organs of the mediastinum (specify where possible)

Further workup

For non-small cell carcinomas, the following algorithm can be applied:

  • Stages IB through IIIA: EGFR mutation analysis.
  • Stages IIIB and IV: Full next generation sequencing panel (DNA and RNA) with PDL-1 immunostaining.


  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.

Main page


  1. 1.0 1.1 Lambe, Gerard; Durand, Michael; Buckley, Anne; Nicholson, Siobhan; McDermott, Ronan (2020). "Adenocarcinoma of the lung: from BAC to the future ". Insights into Imaging 11 (1). doi:10.1186/s13244-020-00875-6. ISSN 1869-4101. 
  2. Barletta, Justine A.; Yeap, Beow Y.; Chirieac, Lucian R. (2010). "Prognostic significance of grading in lung adenocarcinoma ". Cancer 116 (3): 659–669. doi:10.1002/cncr.24831. ISSN 0008543X. 
  3. . Protocol for the Examination of Specimens From Patients With Primary Non-Small Cell Carcinoma, Small Cell Carcinoma, or Carcinoid Tumor of the Lung. Version: Lung Protocol Posting Date: June 2017. College of American Pathologists.