Biopsy is the diagnostic study of choice for adenocarcinoma of the lung. On microscopic histopathological analysis, nuclear atypia, eccentrically placed nuclei, abundant cytoplasm, and conspicuous nucleoli are characteristic findings of adenocarcinoma of the lung. Atypical adenomatous hyperplasia (AAH) is the precursor of peripheral adenocarcinomas. It consists of well demarcated columnar or cuboidal cells with varying degrees of cytologic atypia, hyperchromasia, pleomorphism and prominent nucleoli.

• Biopsy is helpful in the diagnosis of adenocarcinoma of the lung.
  • Fine needle aspiration (FNA)^[1]:
    • CT guided FNA uses a small amount of tissue from a suspected lung tumor or from a lymph node in the chest.
    • FNA may also be obtained during bronchoscopy, along with endobronchial ultrasound, to take samples of lymph nodes around the trachea and bronchi.

• Thoracentesis
  • Thoracentesis may be done to remove fluid from around the lungs to see if it contains cancer cells.
• On microscopic histopathological analysis, nuclear atypia, eccentrically placed nuclei, abundant cytoplasm, and conspicuous nucleoli are characteristic findings of adenocarcinoma of the lung.
• Atypical adenomatous hyperplasia (AAH): is the precursor of peripheral adenocarcinomas. It consists of well demarcated columnar or cuboidal cells with the following features:^[2][3]
  • Varying degrees of cytologic atypia
  • Hyperchromasia
  • Pleomorphism
  • Prominent nucleoli
• As adenocarcinoma is a derivative of mucus producing glands in the lungs, it tends to stain mucin positive.
• Based on differentiation, the tumor may be:
  • Well differentiated (low grade): Normal appearance
  • Poorly differentiated (high grade): Abnormal glandular appearance with a positive mucin stain
• Subtypes^[4]
  • Lepidic predominant:

  • Tumor grows long the alveolar wall

  • Acinar predominant:

  • Berry-shaped glands, smaller than lung acini

  • Papillary predominant:

  • Fibrovascular cores

  • Micropapillary predominant:

  • Nipple shaped projections without fibrovascular cores

  • Solid predominant:

  • Sheet of cells