Preinvasive adenocarcinoma lesion of the lung

Preinvasive lesions for lung adenocarcinoma are a category of small noninvasivenon-invasive lung lesions which are closely related to adenocarcinoma of the lung. They may represent a spectrum of premalignant to low-grade malignant lesions.

The category includes two types of lesions:

• atypical adenomatous hyperplasia (AAH) - smaller, mild-moderate cellular atypia, without evidence of invasion
• adenocarcinoma in situ (AIS) - larger and with more atypia, although still without evidence of invasion

Terminology

In 2011, the International Association for the Study of Lung Cancer, American Thoracic Society, and European Respiratory Society introduced a new classification and terminology for adenocarcinoma of the lung.  In addition to retiring the term "bronchoalveolar carcinoma (BAC)", the 2011 update officially recognized "adenocarinoma in situ" as a distinct entity with excellent clinical prognosis.

Pathology

Atypical adenomatous hyperplasia and adenocarcinoma in situ may be considered a spectrum of premalignant disease, where :

• atypical adenomatous hyperplasia is typically a small (≤5 mm) lesion with mild-moderate cellular atypia, while
• adenocarcinoma in situ lesions are larger, yet still ≤3 cm and demonstrating purely lepidic growth (no invasion). Indeed

Between these two, intermediate cases may be difficult to distinguish ¹.

Findings which indicate more profound genetic alteration, such as non-lepidic (e.g. papillary) growth patterns or tumor necrosis, indicatemoreindicate a more advanced grade of disease.

Radiographic features

Preinvasive lesions of adenocarcinoma are generally not evident by x-ray.

On CT, both atypical adenomatous hyperplasia and adenocarcinoma in situ typically manifest as a round, purely ground glass opacity.

• usually a single opacity ²
  • multiple lesions more common with AIS ²
• "clear" periphery (>85%) ²
  • lobuation, spiculation, pleural indentation are seen in both AAH and AIS, but less common (<21%)
• vacuole sign - internal gas-appearing lucency <5 mm
  • specific to AIS in one 2017 radiology/pathology correlative study (n=80 lesions) ²