Comparative analysis of two methods for assessing the proportion of residual tumor in non-small cell lung cancer after neoadjuvant therapy

The tumor response to neoadjuvant therapy (NAT) in non-small cell lung cancer (NSCLC) defines further treatment tactics and has prognostic value. According to IASLC Guidelines, the amount of viable tumor is expressed as the total percentage of invasive carcinoma obtained by averaging the results for all the fragments studied. In this case, the variability of the tumor bed size in these fragments is not taken into account, which in some cases may lead to overestimation or underestimation of the final results. As an alternative method, it was proposed to calculate the weighted arithmetic mean of the proportion of residual cancer, taking into account the area of the tumor bed in each slide. Objective. Comparative analysis of the accuracy of two methods for assessing the proportion of residual tumor in the NSCLC resection specimens after NAT. Material and methods. The lung resection specimens from 91 patients with NSCLC who had been treated with neoadjuvant therapy were included in this study. Pathological assessment of the percentage of residual tumor in each case was performed by two pathologists on digital images using two scoring methods — the estimation of average percentage and weighted arithmetic mean for residual tumor. Results. The discrepancy between the values obtained using the two techniques in each case ranged from 0% to 32%. A discrepancy of less than 5% in the proportion of viable carcinoma was observed in 77 (85%) patients. More than 10% difference in values was observed in 3 (3%) patients, which was associated with significant variability in the size of the tumor bed area in different slides of one case. Conversion of the morphological regression category after recalculating was observed in 3 (3%) patients. Conclusion. It is more effective to use the calculation of the arithmetic mean value of the residual tumor proportion in routine practice. However, in case of significant variability in the size of the tumor bed area and the proportion of residual carcinoma in each fragment, as well as with the value of the proportion of residual carcinoma close to the threshold value of the MPR (10%) it is recommended to take into account the size of the tumor bed in each slide.