Lymph node involvement according to lung adenocarcinoma subtypes: lymph node involvement is influenced by lung adenocarcinoma subtypes

BACKGROUNDS: Invasive adenocarcinoma subtypes are known to be associated with prognosis; however, the underlying reason remains unclear. To find out the reason, we investigated the possible influence of lymph node (LN) involvement by the constituent histologic subtypes in the tumor and clarified the different prognosis according to the predominant histologic subtypes in the tumor and LN. METHODS: A total of 97 consecutive patients who underwent surgical resection for lung invasive adenocarcinoma between February 2009 and December 2015 were included. We analyzed the associations of the histologic subtypes between the tumor and LN and disease-free survival (DFS) according to the histologic subtypes and predicted the histologic subtype in LN involvement using the component ratio of the predominant histologic subtype in the tumor. A P value <0.05 was considered statistically significant. RESULTS: Acinar and papillary subtypes occupied the majority of the predominant histological subtypes (tumor 73.2%, LN 71.1%). The tumor showed significantly more constituent histologic subtypes than LN (P<0.001). Micropapillary and solid predominant subtype were more common in poorer differentiation (tumor P<0.001, LN P=0.001). The predominant histologic subtype in the tumor was not the same as that in LN and micropapillary and solid predominant subtypes were significantly more prone to LN involvement than other subtypes (P<0.001). Regarding the predominant histologic subtypes in the tumor, there was no significant difference in DFS between micropapillary and solid predominant subtypes and other subtypes. However, regarding the predominant histologic subtypes in LN, micropapillary and solid predominant subtypes had significantly lower DFS than other subtypes (P=0.010). Solid predominant subtype had a significant cutoff value for prediction of the predominant histologic subtype in LN using the component ratio of the predominant histologic subtype in the tumor (cutoff value 12.5%, sensitivity 70.0%, specificity 82.4%, area 0.775, P<0.001). CONCLUSIONS: The present study presented a possible reason of discrepancies in outcomes according to the lung adenocarcinoma constituent subtypes. Micropapillary and solid predominant subtypes had poorer prognosis than other subtypes, which might be explained by being more prone to LN involvement.