Identification of filigree pattern increases the diagnostic accuracy of micropapillary pattern on frozen section for lung adenocarcinoma

Aims The presence of micropapillary (MIP) in early-stage lung adenocarcinoma is associated with a poorer prognosis, especially in patients undergoing sublobectomy. However, data on the sensitivity of frozen section (FS) evaluation of MIP is still limited. We included the concept of a filigree pattern on FS to assess its effect on the diagnostic sensitivity and specificity of MIP, and to verify its prognostic value in stage T1 lung adenocarcinoma. Methods A panel of five pathologists evaluated 125 patients with T1 lung adenocarcinoma from January to February 2014 as a study cohort, and 151 patients from January to February 2020 as a validation cohort. The diagnostic accuracy of the filigree and classical micropapillary (cMIP) pattern on FS was investigated. Results The diagnostic sensitivity of the MIP pattern on FS increased from 43.2% to 65.3% and 56.8% to 81.1% in the study cohort and validation cohort, respectively, and both with good specificity. Filigree not only increased the sensitivity of identifying MIP when there was an absence of cMIP, but also increased the sensitivity when the presence of a minor amount of cMIP. The almost perfect agreement among five pathologists was reached on cMIP and substantial agreement was reached on the filigree in the two cohorts. Moreover, the cMIP and filigree were both correlated with poorer recurrence-free survival (p(cMIP) = 0.003; p(filigree) = 0.032) and overall survival (p(cMIP) = 0.004; p(filigree) = 0.005). Conclusions The identification of a filigree may improve the diagnostic sensitivity of the MIP pattern on FS. FS was feasible for the detection of filigree and cMIP patterns in stage T1 lung adenocarcinomas.