Pulmonary: Practice Question

A 54 year old male is found to have a lung mass which is removed by wedge resection. It is 2 cm in maximum dimension, does not show lymphovascular or stromal invasion, and has a lepidic growth pattern. By IHC, the mass is positive for CK7, TTF-1 and Napsin A. What is the most likely diagnosis?
  1. Adenocarcinoma in situ
  2. Minimally Invasive Adenocarcinoma
  3. Invasive adenocarcinoma, lepidic predominant
  4. Invasive mucinous adenocarcinoma
  5. Squamous cell carcinoma
Show Answer and Explanations

Adenocarcinoma in situ — Correct answer

Correct. In the lung, adenocarcinoma in situ (formerly bronchoalveolar carcinoma) is <= 3 cm in size and must have a lepidic growth pattern. Any invasion, necrosis or non-lepidic growth patterns disqualify this diagnosis. The most common subtype is non-mucinous.

Minimally Invasive Adenocarcinoma

Incorrect. Minimally invasive adenocarcinoma in the lung is defined as tumors with lepidic or predominantly lepidic growth, <= 3 cm in size, with <= 5 mm of invasion into the stroma.

Invasive adenocarcinoma, lepidic predominant

Incorrect. Lepidic predominant invasive adenocarcinoma is > 3cm in size, or shows necrosis, > 5mm stromal invasion, lymphatic, vascular or pleural invasion, and has a lepidic growth pattern.

Invasive mucinous adenocarcinoma

Incorrect. Invasive mucinous adenocarcinoma is > 3cm in size, or shows necrosis, > 5mm stromal invasion, lymphatic, vascular or pleural invasion and is mucin producing.

Squamous cell carcinoma

Incorrect. Squamous cell carcinoma is positive for p63 and CK5/6.

Summary

Summary: Bronchoalveolar carcinoma is now called adenocarcinoma in situ. It is <= 3cm and has a lepidic growth pattern. Minimally invasive adenocarcinoma is defined as tumors with lepidic or predominantly lepidic growth, <= 3 cm in size, with <= 5 mm of invasion into the stroma.
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