51. Lepidic adenocarcinoma

Staining: HE

Overview of the slide

Organ: Lung

Description:

The slide has two zones. The lower zone shows healthy, unaffected lung parenchyme. The upper zone shows normal structure of the alveoli, however the insides of the alveoli are lined by tumor cells.

Diagnosis: Lepidic adenocarcinoma

Risk factors: Asian ethnicity, smoking Genetic mutations

Theory:

Five types of lung adenocarcinomas exist:

• Papillary type
• Acinar type
• Solid type
• Micropapillary type (worse prognosis)
• Lepidic type (best prognosis)

This histology slide shows a “lepidic” growth pattern, which is the pattern where the tumor cells line the alveolar walls instead of invading the interstitium. The alveolar structure is therefore maintained. It’s technically an adenocarcinoma in situ because it hasn’t passed the basement membrane yet. Like other lung adenocarcinoma it's associated with mutations in EGFR, KRAS, ALK, PDL-1.

The lepidic growth pattern. See how the cancer cell create a lining of the walls of the alveoli.

Check out the pleomorphism of the tumor cells (anisochromasia, anisocytosis, anisonucleosis). Note that the tumor cells have large, pale cytoplasm. They belong to an adenocarcinoma after all!