520
A study following large patient groups on theophylline and a combination of theophylline and steroids might clarify the risk of ulcer formation in patients being treated with these medications for asthma.
 adverse event: risk 
Please tell me event type and its trigger word from given type options. Output format is "type: trigger".  Option: adverse event, potential therapeutic event 
Text: {0} 
Answer:
 adverse event: risk 