10617 Background: Whether trastuzumab should be continued after tumor progression remains unknown.We describe the activity of successive trastuzumab-containing regimens in patients with HER2-overexpressing metastatic breast cancer, as well as the response rate, time to progression and predictive factors for response. Methods: Descriptive retrospective study of trastuzumab activity in patients with HER2-overexpressing metastatic breast cancer treated at our hospital from 10/1999 to 07/2005. Results: 93 consecutive patients were evaluated obtaining an objective response rate (OR) for first-time administration of trastuzumab of 46.2%; stable disease (SD) 24.7%; clinical benefit (CB) 71%. Median time-to-progression (TTP) was 5 months (range: 1–39+). A total of 47 pts (50.5%) received a second trastuzumab-containing regimen with an OR of 29.8%; SD 21.3%; CB 51.1%; TTP 4 months (range: 1–31). A total of 21 pts (22.6%) received a third trastuzumab-containing regimen; OR 38.1%; SD 23.8%; CB 61.9%; TTP 4 months (range: 1–30+). A total of 10 pts (10.8%) received a fourth trastuzumab-containing regimen; OR 20%; SD 20%; CB 40%; TTP 4 months (range: 1–37). 5 pts (5.4%) received a fifth trastuzumab-containing regimen; OR 0%; SD 60%. Age < 45 years is a significant prognostic factor (p: 0.005, 95% CI, OR 5.6 (1.5–20.6)). A better response rate in the successive trastuzumab-containing regimens was observed, when there was a response in the first regimen: p = 0.04; 95% CI; OR 3.84 (1.07–14.65). With a follow-up of 16,5 months 45 pts (48,4%) are alive. Conclusions: Trastuzumab-containing therapies beyond disease progression in metastatic breast cancer show activity. There were more responses in younger pts. Those pts who had a previous response to trastuzumab therapy were more likely to respond to successive trastuzumab-containing regimens. Additional controlled studies are needed to test this approach. No significant financial relationships to disclose.

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500 Background: PPI are widely used in pts with cancer. PPI are associated with anti-inflammatory properties and direct effects on neutrophils and monocytes that might prevent inflammation. We investigate the role of PPI on outcomes of pt receiving ICI in mUC. Methods: Medical records from pts with mUC treated with ICI from May 2013 to May 2019 using a multi-institutional database was evaluated. Use of PPI was defined: 30 days prior, during the treatment and 30 days after the last dose of ICI. ORR were assessed according to RECIST v1.1. The X2 test was used to determine differences in rates. PFS and OS were estimated using Kaplan-Method and long rank test was used to assess differences between groups. All analyses were performed using SPSS v21. Results: Overall, 115 pts received therapy with ICI. Of these pts, 20 were not included due to the absence of information about PPI. Thus, 95 pts were included for the analysis. 50 (52.6%) pts received PPI. Median age was 68 years, 79 pts (83.2%) were male, 78 pts (82.1%) had ECOG PS 0-1, 20 pts (21.1%) had liver metastasis and 36 pts (37.9%) received ICI treatment as frontline therapy. ICI prescribed were atezolizumab (58.9%), pembrolizumab (17.9%), durvalumab (12.6%), nivolumab (6.3%) and durvalumab/tremelimumab (4.2%). Pts with no PPIs use had higher ORR (CR [8.9%] +PR [14.4%]) compared to those pt who use PPIs (CR [4.4%] + PR [8.9%]) (P=0.197). Median PFS was 10.05 mo (95% CI: 3.86-16.27) for non PPI users and 3.87 mo (95% CI:1.84-5.91) for PPI users (P=0.04). Median OS was 19.71 mo (95% IC:8.93-30.49) for non PPI users and 7.9 mo (4.4-11.45) for PPI users (P=0.072). Conclusions: We have observed shorter PFS and trend toward lower OS and ORR for PPI users. The real impact of PPI should be confirmed in prospective studies.

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