( CNN ) -- Juanita Castro Ruz , sister of former Cuban leader Fidel Castro and Cuban President Raul Castro , is undergoing radiation treatment in Miami , Florida , for lung cancer , her spokeswoman told CNN . Castro underwent surgery more than a month ago in a Miami hospital to remove a tumor in her lung , her biographer and spokesperson , journalist Maria Antonieta Collins , said . Collins said Castro is recovering well and her diagnosis is very good . `` I am in the best medical hands , receiving the proper treatment , '' Castro said on her website . `` It 's a serious condition , but I 'm not at the side of my grave . '' Castro released an autobiography last year titled `` My Brothers Fidel and Raul , the Secret History . '' The notoriously private Castro decided to go public about her condition unlike her ailing brother Fidel Castro . Fidel Castro fell ill in 2006 of a as yet unspecified stomach ailment . Raul Castro formally took over as President in 2008 . CNN 's Robert Lenz contributed to this report .
Juanita Castro Ruz undergoes radiation treatment in Miami , Florida , for lung cancer . She had surgery more than a month ago to remove tumor in lung , biographer says . `` It 's a serious condition , but I 'm not at the side of my grave , '' Castro says on her website .