<qa>  What was the lowest frequency of ulcers in the omeprazole group?To date, two large clinical trials have been performed to evaluate the effectiveness of proton pump inhibitors in preventing mucosal injury. The first trial selected 182 patients with breast cancer 77 pts or colon cancer 105 pts who were receiving cyclophosphamide, methotrexate and 5-FU CMF, or 5-FU, respectively. These patients were randomized to receive either omeprazole 20 mg daily, misoprostol a prostaglandin analogue 400 mg twice daily, or placebo once daily for two full courses of chemotherapy 56 days. Endoscopic evaluation EGD was performed one week prior to initiation of chemotherapy and one week after the end of the second cycle of chemotherapy comparing the number of erosionsulcers in the stomach and duodenum. The omeprazole group had a lower frequency and degree of erosions compared to placebo and misoprostol. Symptoms of epigastric pain and heartburn were also significantly less in the omeprazole patients. A second study performed by the same group evaluated patients with breast or colon cancer n228 receiving either CMF or 5-FU. These patients were randomized to receive omeprazole 20 mg daily, ranitidine 300 mg daily a H2 blocker, or placebo once daily for 56 days. EGD was performed as above, before cycle 1 and after cycle 2 of chemotherapy. The omeprazole group experienced the lowest frequency of ulcers n2, followed by the ranitidine group n8, and the placebo group n18. Symptoms of epigastric pain or heartburn were also significantly less in the omeprazole arm n11 compared to the ranitidine n13 or placebo n24 arms. Chemotherapy was delayed in the placebo and ranitidine group, but not in the patients receiving omeprazole. These two trials demonstrate the ability of a proton pump inhibitor omeprazole to limit the mucosal injury induced by chemotherapy. Protecting the mucosa from damage also appeared to significantly decrease the frequency of upper GI symptoms. It should be noted that nausea or vomiting was not assessed in either trial since various antiemetics were given during chemotherapy. 