Lung cancer invading the fissure to the adjacent lobe: more a question of spreading mode than a staging problem.

Objectives: Lung cancer invading beyond the interlobar pleura, classified as T2a in the new TNM, is a rare entity with a poor outcome. Our purpose was a better understanding of the mechanisms of this particular behaviour and its prognostic value.
Methods: Patients who underwent surgery between 1984 and 2007 were reviewed. We focused on T1 and T2 tumours. Tumours not traversing the pleural elastic layer were defined as PL0, extending through the layer as PL1 and extending to the surface of the visceral pleura as PL2. We considered three groups: group 1, tumours invading the lobar fissure, group 2, PL0-tumours and group 3, PL1 + PL2 tumours and studied their pathology and prognostic characteristics.
Results: The distribution was as follows: group 1 n = 154, group 2 n = 2310 and group 3 n = 651. Pneumonectomy was necessary in 55.2% and bilobectomy in 19.5% of group 1, and N-involvement was present in 55.8% (significantly more than other groups). The mean tumour size (42.7 ± 12 mm) was bigger in group 1. Post-operative mortality was as follows: -5.2, -3.5 and 3.2% in groups 1, 2 and 3, respectively (P = 0.49). Five-year survival rates were: group 1: 38.9%, group 2: 52.5% and group 3: 43.4%; P = 0.00002. Survival was not different between groups concerning pN1 and pN2, but poorer in groups 1 and 3 than in group 2 in pN0 patients, P = 0.0057. Survival was 48.1, 37.9 and 38.4% for tumours between 31 and 70 mm in groups 2, 1 and 3, respectively, P = 0.0024 (but P = 0.65 between groups 1 and 3). Pneumonectomy was a poor prognostic factor in all groups, but survival between pneumonectomy and bilobectomy was not different in group 1. Multivariate analysis confirmed intralobar invasion to be an independent factor of poor prognosis, as well as visceral pleura invasion.
Conclusions: Tumours invading through the fissure have a significant effect on long-term survival in the first stages of lung cancer but also in all stages because of their size and important locoregional spread. Their prognostic value is due to pleural invasion, whose role in lung cancer dissemination is worth further research.