Adenocarcinoma in situ of the lung

Last revised by Prashant Kandel on 13 Oct 2022

Adenocarcinomas in situ (AIS) of the lung refer to a relatively new entity which falls under the spectrum of pre-invasive lesions of the lungs. This entity partly replaces the noninvasive end of the previous term bronchoalveolar carcinoma. Adenocarcinoma in situ is defined as a localized adenocarcinoma of <3 cm that exhibits a lepidic growth pattern, with neoplastic cells along the alveolar structures but without stromal, vascular, or pleural invasion 1.

AISs are localized adenocarcinomas of ≤3 cm, with no growth pattern other than lepidic, with neoplastic cells along the alveolar structures but without stromal, vascular, lymphatic, or pleural invasion, and no features of necrosis 6

There are three histopathological subtypes, the most common is non-mucinous, with mucinous or mixed subtypes being rarely found. 

While adenocarcinoma in situ is usually seen as a pure ground-glass nodule or a part-solid lung nodule, there can be overlap among the imaging features of atypical adenomatous hyperplasia, adenocarcinoma in situ, and invasive adenocarcinoma of the lung 1.

Adenocarcinomas in situ are commonly associated with PET false-negative results. FDG PET-CT is recommended when assessing subsolid ground-glass lung lesions that have a solid component measuring more than 8 mm 5

Adenocarcinoma in situ carries an excellent prognosis, with reported survival rates of 100% following complete tumor resection 6.

For follow-up guidelines consider - Fleischner Society pulmonary nodule recommendations

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Cases and figures

  • Case 1
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  • Case 2: probable
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