Main characteristics of all studies included in the systematic review.

Data are reported as mean ± SD or as median (range). Abbreviations: A, adenocarcinoma; NR, not reported; S, squamous carcinoma; SA, adenosquamous carcinoma. *Data for the two groups were not reported separately. ▴Cases of SA were not reported separately from the other types of histology findings, so they have been included here as S/A/SA+Other types.