Size and predictive factors of microscopic tumor extension in locally advanced non-small-cell lung cancer.

Abstract

PURPOSE\nRadiation therapy for locally advanced non-small cell lung cancer (NSCLC) should treat the whole tumor, including its microscopic extensions, while protecting adjacent organs at risk as much as possible. The aim of our study is to evaluate the size of microscopic tumor extension (MEmax) in NSCLC, and search for potential predictive factors.\n\n\nMETHODS AND MATERIALS\nWe retrospectively selected 70 patients treated with post-operative radiation therapy for a NSCLC with N2 nodal status, then 34 additional patients operated for a squamous cell lung cancer with N1 or N2 nodal status. On the digitized slides originating from the resected tumors of these 104 patients, we outlined the border of the tumor, as seen with the naked eye. We then searched for microscopic tumor extension outside of these borders, with a magnification as high as x 40, and measured the maximum size of MEmax.\n\n\nRESULTS\nThe median MEmax in the whole cohort was 0.85 mm [0-9.95]. The MEmax was less than 5.3 mm in 95% of adenocarcinomas (6.5 mm in the subgroup without neo-adjuvant chemotherapy) and less than 3.5 mm in 95% of squamous cell carcinomas (3.7 mm in the subgroup without neo-adjuvant chemotherapy). After multivariate analysis, the factors associated with the size of MEmax were vascular invasion (p=0.0002), histologic type, with a wider MEmax for adenocarcinomas in comparison with squamous cell carcinomas (p=0.002), tumor size, which was inversely related with the size of MEmax (p=0.024), and high blood pressure (p=0.03). Macroscopic histologic tumor size was well correlated with both radiologic tumor size on a mediastinal setting CT (correlation coefficient of 0.845) and on a parenchymal setting CT (correlation coefficient of 0.836).\n\n\nCONCLUSIONS\nThe Clinical Target Volume margin, accounting for microscopic tumoral extension, could be reduced to 7 mm for adenocarcinomas and 4 mm for squamous cell carcinomas.