Lepidic-predominant adenocarcinoma of the lung

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Lepidic-predominant adenocarcinoma (LPA) of the lung, formerly known as non-mucinous bronchoalveolar carcinoma, is a subtype of invasive adenocarcinoma of the lung characterized histologically when the lepidic component comprises the majority of the lesion.

Terminology

The category of 'lepid predominant adenocarcinoma' now replaces 'non-mucinous bronchoalveolar carcinoma' of the lung.

In 2011, the International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS), and European Respiratory Society (ERS) introduced a new classification and terminology for adenocarcinoma of the lung, which is now divided into 'preinvasive', 'minimally invasive', and 'invasive'.

The term bronchoalveolar carcinoma (BAC) has been retired, and it is recommended that all invasive adenocarcinomas be classified in terms of the "predominant" comprising histology . Both mucinous and non-mucinous adenocarcinomas typically consist of a mixture of histologic patterns, but reporting of the predominant subtype is specifically recommended for non-mucinous lesions, with all mucinous tumors placed in a separate category.

Pathology

It is often defined as a  tumor of > 3 cm in total size and/or has > 5 mm lymphatic, vascular or pleural invasion with a non-mucinous lepidic predominant growth pattern .

Invasive adenocarcinoma is defined as a lesion with > 5 mm of invasion into the normal surrounding lung (i.e. lymphatics, pleura, or blood vessels) and/or the presence of tumor necrosis on the basis of histology of the surgical resection specimen. The non-mucinous disease is further assessed for any histologic patterns within the lesion (lepidic, acinar, papillary, micropapillary, and solid growth), and the "predominant" subtype is reported .

Thus, lepidic predominant invasive adenocarcinomas show a predominance of bland pneumocytic-type neoplastic cells with growth along with normal structures e.g. alveoli.

Radiographic features

CT

While non-specific CT features for this subtype have been reported (as of 2018), studies suggest some features may show an increased chance of invasiveness associated with these tumors :

  • increasing maximum diameter of the whole lesion (ground glass and solid component) 
  • larger diameter of the solid component / higher visual estimated percentage solid component compared to the whole lesion