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Visceral pleura and pN involvement in lung cancer.

Adachi et al. [1] studied visceral pleural involvement (VPI) in 639 patients collected from 9 hospitals and reported that VPI was present as PL1 (tumour invading beyond the elastic layer but not exposed on the visceral pleura) in 135 patients and PL2 (tumour invading and exposed on the visceral surface but not involving adjacent anatomical structures) in 42. They compared them with the 462 other PL0 (tumour within the lung parenchyma not reaching the elastic layer) patients. The 5-year survival rate differed significantly between PL0 (75.9%) and PL1 patients (63.6%), but not between PL1 and PL2 (54.1%). Those differences persisted in 502 pN0 patients (96 PL1, 27 PL2) and in 69 pN1 (18 PL1, 12 PL2), but were not significant in the latter. The pN2 patients (44 PL0, 21 PL1 and 3 PL2) represented 10.4% in the study. On multivariate analysis, VPI was an independent predictor of survival. When reviewing a similar VPI population from a two-hospital database [2], we found 1687 PL0, 255 PL1 and 180 PL2 patients with 5-year survival rates of 61.2, 60.3 and 41.9%, respectively (P = 0.000034), but no difference in survival between PL0 and PL1 patients. The difference existed in pN0 patients but not in case of pN involvement. The pN involvement was similar in PL1 and PL0 patients (pN1 12.2%, pN2 18.4% and pN1 16.8%, pN2 19.1%, respectively), but more important in PL2 (pN1 18.9% and pN2 28.3%). On multivariate analysis, VPI was not a predictor of survival. The results of Adachi et al. [1] lead them to suggest that the presence rather than the extent of VPI had an impact on survival in patients with pN0 and pN1, which does not correspond with our findings. These differences between their work and ours may be due to the weak statistical power of their study, which was relatively small as they suggested, but also probably to the selection of their population. Clinical N2 patients might have undergone induction therapy and be excluded from the study. In such a case, studying the role of VPI in pN involvement without including clinical N2 that could benefit from a curative surgery might have biased the results. The pleura effectively plays an important role in lung cancer dissemination. Its involvement affects pN but to a greater extent in pN2 than in pN1 patients [2].