final report of my wife,of the usg abdomen & pelvis ,dated;16.05.2012 revealed multiple enlarged periportal,aortocaval,left paraaortic & mesentric nodes.attending oncologist doctor prescribed tablet Letrozole 2.5mg,once daily,for 3 months.intake of the medicine was started on 25.05.2012. since 5 days she is having vomiting tendency most of the time & vommits 2 or 3 times everyday. why is she having vomiting tendency?