Abstract only 442 Background: There are no formal guidelines for the management of GI cancer pts with lung-exclusive or lung-predominant metastases (LM), which generally take a more indolent course than metastatic disease occurring at other anatomic sites. We performed a retrospective analysis at a high-volume tertiary care center to evaluate host and tumor characteristics of this pt population, describe treatment approaches, and model patterns and rates of growth. Methods: Eligible pts were identified through Cancer Center registry data, provider recall, and electronic record review. Criteria included LM occurring either synchronously (SLM) or metachronously (MLM) w/primary cancer diagnosis; nodal, but not visceral or peritoneal, mets allowed. Data re: demographics, tumor characteristics, and rx modalities were collected. We reviewed all eligible CT +/- PET scan reports to gather data on #, location, and size of pulm mets, with all images subsequently reviewed by an independent radiologist. Up to 5 pulm mets were tracked through each pt’s clinical course. Growth rate was estimated using a linear mixed model analysis considering patients as the random. Results: Forty pts were identified between 9/2009 - 12/2019 (23 F/17 M; 28 white/7 Asian/5 other/multi; median age 62 y.o.; n = 15 w/tobacco hx). Tumor types: pancreatic (n = 18), colorectal (n = 12), hepatobiliary (n = 7), other (n = 3). SLM vs MLM:13/27; intact vs resected primary = 16/24. Median time from orig cancer dx to onset of MLM = 16 mos (range, 1 to 60 mos). No. of pulm mets at 1st appearance: 1 (n = 7); 2-5 (n = 17); 6-10 (n = 16). Median size of largest pulm met at 1st appearance = 6 mm (range, 0-39 mm); avg growth rate of largest pulm met = 0.18 mm/month (95% CI, 0.08-0.27). Avg growth rate of up to 5 largest lesions (sum) = 0.35 mm/month (95% CI, 0.07-0.64). Median f/u time prior to rx initiation for MLM = 172 days (range, 25-1547 days); 18 pts developed additional mets during their observation period. Rx modalities for LM: surg (n = 6), radiation (n = 18), systemic rx (n = 32). Addn details specific to cancer type, progression patterns, and pt outcomes will be presented at the meeting. Conclusions: The natural hx of LM varies across the spectrum of GI malignancies. Further larger-scale efforts to define patterns of growth of LM for different GI cancers, informed by size, #, and clinical/molecular features, are needed to guide appropriate timing and selection of rx as well as surveillance strategies.