Background: T-DXd is an antibody-drug conjugate composed of an anti-HER2 antibody, cleavable tetrapeptide-based linker, and topoisomerase I inhibitor payload. Early studies have shown promising activity in advanced HER2-expressing tumors. DESTINY-CRC01 (DS8201-A-J203; NCT03384940) is a phase 2, open-label, multicenter study of T-DXd in pts with HER2-expressing mCRC. Methods: Pts with centrally confirmed HER2-expressing, RAS–wild type mCRC that progressed on ≥ 2 prior regimens received T-DXd 6.4 mg/kg every 3 weeks (q3w) in 3 cohorts (A: HER2 IHC 3+ or IHC 2+/ISH+; B: IHC 2+/ISH−; C: IHC 1+). The primary endpoint was confirmed objective response rate (ORR) by independent central review in cohort A; secondary endpoints included, disease control rate (DCR; CR + PR + SD), duration of response (DOR), progression-free survival (PFS), overall survival (OS), and ORR in cohorts B and C. Results: At data cutoff (Aug 9, 2019), 78 pts (A, 53; B, 7; C, 18) had received T-DXd. Median age was 58.5 y (range, 27-79 y), 52.6% of pts were male, and 89.7% had left colon or rectum cancer; median number of prior regimens was 4 (range, 2-11); all pts had prior irinotecan. Median treatment duration was 3.5 mo (95% CI, 2.1-4.3 mo; cohort A, 4.8 mo [95% CI, 3.9-5.8 mo]); 38.5% of pts remained on T-DXd treatment. The confirmed ORR was 45.3% (24/53 pts; 95% CI, 31.6%-59.6%) in cohort A, including 1 CR and 23 PRs; median DOR was not reached (95% CI, 4.2 mo-NE). The ORR in pts with prior anti-HER2 treatment was 43.8% (7/16 pts; 95% CI, 19.8%-70.1%). The DCR was 83.0% (44/53 pts; 95% CI, 70.2%-91.9%); median PFS was 6.9 mo (95% CI, 4.1 mo-NE); median OS was not reached. No responses were observed in cohorts B or C. Grade ≥ 3 treatment-emergent adverse events (TEAEs) occurred in 61.5% of pts (48/78); the most common (≥10%) were decreased neutrophil count (21.8%) and anemia (14.1%). Seven pts (9.0%) had TEAEs leading to drug discontinuation. Five pts (6.4%) had interstitial lung disease (ILD) adjudicated by an independent committee as related to T-DXd (2 grade 2; 1 grade 3; 2 grade 5 [the only drug-related deaths]). Conclusions: Overall, T-DXd 6.4 mg/kg q3w demonstrated remarkable activity in pts with HER2-expressing mCRC refractory to standard therapies, with a safety profile consistent with previous results. ILD is an important risk and requires careful recognition and intervention. Clinical trial information: NCT03384940.