Histological growth pattern as a potential marker of oligometastatic disease in patients operated for colorectal liver metastases

e15093 Background: The identification of oligometastatic profile in patients with resectable colorectal liver metastases (CRLM) would represent a major progress to improve selection for surgery. Currently, in the absence of biomarkers, the most reliable method to identify oligometastatic (OLM) and non-oligometastatic (NOLM) tumors relies on the oncological outcome after metastases-targeted surgery. The histological growth pattern (HGP) of CRLM, defined as desmoplastic (dHGP) or replacement (rHGP), has recently been shown to have prognostic value. We analyzed HGP in a series of patients operated for CRLM, characterized as OLM in case of prolonged postoperative recurrence-free survival (RFS) or NOLM in case of rapid postoperative relapse. Methods: In 357 patients operated for CRLM, we identified OLM patients as those with RFS≥5 years (N = 64), and NOLM patients as those with RFS < 1 year (N = 77). Clinicopathologic and surgical parameters were analyzed. In each CRLM, HGP was assessed in archival H&E stained tissue sections, according to international consensus guidelines. Proportions of rHGP and dHGP were determined in each metastasis. In case of multiple metastases, the mean HGP was calculated in each patient. Patients were categorized as pure (> 95% rHGP or dHGP) or dominant phenotypes (> 50% rHGP or dHGP, of the entire tumor-liver interface). Results: Preoperative characteristics of primary tumor and CRLM, and surgical data were identical in OLM and NOLM groups. In a first set of analyses, HGP was determined in 39 OLM and 52 NOLM patients. Pure dHGP was observed in 54.3% of OLM and 17.3% of NOLM patients (p = 0.001). Pure rHGP was similarly distributed among OLM and NOLM groups. Sixty-nine% of the OLM patients displayed a dHGP-dominant phenotype, whereas 57.7% of the NOLM patients presented with a rHGP-dominant phenotype (p = 0.02). Conclusions: These results confirm the potential prognostic value of HGP in patients operated for CRLM. dHGP, associated with angiogenesis and inflammation, could represent a (surrogate) marker for oligometastatic progression, whereas rHGP appears strongly associated with rapid postoperative relapse.