To better understand the relationship between the maximum tumor diameter and the most distant micrometastases in different types of non-small cell lung cancer (NSCLC) and to provide histological evidence for the delineation of clinical target volume (CTV) from gross tumor volume.

We retrospectively studied the pathological specimens from 113 surgically treated NSCLC patients (44 squamous cell carcinoma patients and 69 adenocarcinoma patients) who were admitted to our hospital from 2014 to 2015. The maximum tumor diameter was determined by a combination of gross and microscopic measurements. Micrometastases were microscopically determined. The distances between the tumor edges and micrometastases outside the tumor boundaries were measured by an ocular micrometer followed by a calculation. Quantitative data were analyzed by t test, and qualitative data were analyzed by logistic regression.

The regression relationship between the maximum tumor diameter and micrometastases was significant in the adenocarcinoma group, but not significant in the squamous cell carcinoma group (P=0.151). The association between the presence or absence of lymph node metastasis and the most distant micrometastasis was significant in the adenocarcinoma group, but not significant in the squamous cell carcinoma group (P=0.597). No association between the degree of tumor differentiation and the most distant micrometastasis was observed in either group (P=0.113). The average measurement of the most distant micrometastases was 2.94 mm in the adenocarcinoma group, with 7.5 mm as the distance to cover 95% of the most distant micrometastases. To reach the same coverage, 4 mm was needed for tumor size smaller than 3 cm, 6 mm for those between 3 cm and 5 cm, and 7.5 mm for those larger than 5 cm. The average measurement of the most distant micrometastases was 2.69 mm in the squamous cell carcinoma group, with 6 mm as the distance to cover 95% of the most distant micrometastases.

For NSCLC, the most distant micrometastasis of adenocarcinoma is associated with the maximum tumor diameter and presence or absence of lymph node metastasis, and the CTV should thus be adjusted accordingly; no relevance between the most distant micrometastasis and maximum tumor diameter is observed in squamous cell carcinoma; there is no relationship between the most distant micrometastasis and the degree of tumor differentiation in adenocarcinoma and squamous cell carcinoma.

Lung neoplasms/surgery; Microextension/pathology; Clinical target volume; Lung neoplasms/three-dimensional conformal radiotherapy