Pulmonary Adenocarcinoma Patterns

The good, the bad and the ugly

C. Black 5-23-2014CTOP retreat

2004 WHO

• 4 major patterns of ADC– Bronchioloalveolar– Acinar– Papillary– Solid– Mixed (most common)

2011 IASLC/ATS/ERS ADC re-classification

Recommendation

• Discontinue use of the term BAC1. Being used as ADC in-situ2. Minimally invasive ADC3. Invasive ADC with lepidic pattern4. Invasive mucinous ADC

2011 IASLC/ATS/ERS ADC re-classification

Recommendation – Mixed sub-type discontinued– Predominant pattern used– Percentage estimates for mixed tumors

2011 IASLC/ATS/ERS ADC re-classification

• Recommendation strength – Weak

• Low evidence for reproducibility….

Reproducibility of histopathological subtypes and invasion in pulmonary adenocarcinoma. An international interobserver study

Modern Pathology (2012)

• 26 pathologists, 115 cases• micro photographic images of ADCs• Mix of typical and difficult cases• Mean kappa scores: 0.77+/-0.07 typical 0.38+/-0.14 difficult• Highest correlation for solid and least for

micro papillary

• Identification of Invasion versus in-situ(28 pathologists/64 images)

Kappa scores: 0.55+/-0.06 typical cases 0.08+/-0.02 difficult cases

Consistent subdivisions suggesting educational bias

2011 IASLC/ATS/ERS ADC re-classification

• Recommendation

• Micropapillary ADC – added as major pattern

Current ADC Patterns

1. Acinar2. Non-mucinous lepidic (former BAC)3. Micropapillary4. Papillary5. Solid

Acinar

AIS (non-mucinous)

AIS• Non-mucinous lepidic• Localized small (≤3 cm) adenocarcinoma• Growth restricted to neoplastic cells along

preexisting alveolar structures (lepidic growth)• Lacking stromal, vascular, or pleural invasion

A, lepidic growth with a small (<0.5 cm) central area of invasion. B, To the left is the lepidic pattern and on the right is an area of acinar invasion. C, These acinar glands are invading in the fibrous stroma.

IASLC, JCO 2011

Microinvasive adenocarcinoma

Micropapillary

• Histopathology, Volume 46, Issue 6, pages 677–684, June 2005

Human PathologyVolume 39, Issue 3, March 2008, Pages 324–330

Papillary

Solid

• “In patients with multiple lung adenocarcinomas, we suggest comprehensive histologic subtyping may facilitate in the comparison of the complex, heterogeneous mixtures of histologic patterns to determine whether the tumors are metastases or separate synchronous or metachronous primaries (weak recommendation, low-quality evidence)”.

CTOP Case

Tumor 1, 1.3 cm

Tumor 2, 1.0 cm

• Good – AIS, Microinvasive

• Bad – Acinar, Papillary

• Ugly – Solid , Micropapillary