Metastatic potentiality of micropapillary and conventional histological patterns: a comparative study of 82 pulmonary...

The recently described micropapillary pattern (MPP) is potentially a strong unfavorable prognostic marker for adenocarcinoma of the lung. None of the previous studies compared the association to nodal metastasis between conventional histological patterns and MPP.

Histological patterns (1=solid, 2=poorly formed acinar 3=well formed acinar, 4=papillary, 5=bronchioloalveolar), and MPP were semiquantitatively evaluated in 82 pulmonary adenocarcinomas and correlated with nodal status.

Mean percentages of pattern 1 and 2 are higher in node positive (N+) group (33.9% vs 19.3%, p=0.046; and 20.8% vs 13.4%, p=0.19, respectively). Analysis of the combined amount of pattern 1 and 2 revealed increased statistical significance (54.6% vs 32.5%, p=0.007). Mean percentages of pattern 3, 4 and 5 tended to be lower in N+ group (22.8% vs 29.4%, p=0.24; 2.8% vs 6.2%, p=0.33; and 17.9% vs 31.2%, p=0.053, respectively). Analysis of the combined amount of pattern 3, 4 and 5 showed increased statistical significance (43.3% vs 66.8%, p=0.005). Mean percentage of MPP was higher in N+ group (28.3% vs 11.3%, p=0.0007) after excluding the cases with more than 80% percent of pattern 1 and 2. The criterion of MPP > or = 20% or combined pattern 1 and 2 > 50% of tumor is strongly associated with nodal metastasis (p=0.0015). Pattern 1 has the highest rate of correspondence of having a similar pattern in metastases (18/26, 69.2%), followed by MPP (10/19, 52.6%), and pattern 2 (12/23, 52.2%).

MPP has comparable metastatic impact to the solid and the poorly formed acinar patterns and it is prognostically informative to document the presence or absence of the solid plus poorly formed glandular pattern > 50% and MPP > or = 20% when histological subtype is evaluated.