Clinical prognostic factors in surgically treated oligometastatic non-small cell lung cancer: a systematic review

Since the concept of oligometastatic (OM) disease was introduced in the oncological scenario of non-small cell lung cancer (NSCLC), these patients progressively became a new category of stage IV NSCLC in whom the multimodality approach, including surgery, may improve prognosis. This systematic review aimed to investigate the clinical prognostic factors in OM-NSCLC surgically treated with radical intent.

This systematic review is reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Cochrane's Collaboration Tool was used to determine the risk of bias for the included studies' primary outcome. A search strategy using a combination of free-text words, relevant MeSH headings and appropriate restrictions (time limit: from January 1997 to March 2020, language: English) was designed. Potentially qualified papers were subjected to an in-depth full-text examination after preliminary title/abstract screening to identify studies for inclusion in the systematic review. Data extracted included: study characteristics, baseline patient characteristics, primary and secondary outcomes. The Cochrane's Collaboration Tool was used to determine the risk of bias for included studies' primary outcome. The risk of bias due to incomplete outcome data was evaluated at an outcome level. However, at the study stage, the possibility of bias due to sequence generation, allocation concealment, blinding, selective reporting, or funding was assessed. Two independent observers calculated the probability of bias, and differences were resolved through dialogue and consensus.

Nine studies were selected. Overall survival (OS) was 51.8 months and varied from 21.1 to 60 months, but results were not statistically significant. Positive prognostic factors for survival were cessation of smoking, age <60, a histologic grade of G1/G2, pN0. The presence of extra-brain OM and multiple metastases negatively affected survival.

For otherwise stable patients with a single organ site with synchronous (or metachronous) extrathoracic M1 disease and no intrathoracic lymph node involvement, aggressive treatment should be used in the absence of randomized evidence to help determine the effective management of OM-NSCLC.