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In a lepidic adenocarcinoma, the invasive component consists of at least one focus greater than 0.5 cm in largest dimension and can show one or more of the following features: 1) histologic types other than lepidic pattern (e.g. acinar, papillary, micropapillary, or solid); 2) tumor cells associated with desmoplastic stroma; 3) vascular or pleural invasion; 4) spread through air spaces.

If the invasive focus is smaller than or equal to 0.5 cm, the diagnosis of minimally invasive adenocarcinoma may be entertained provided certain other criteria are met.

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