CREATE TABLE table_37898 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" TEXT, "Result" TEXT)

Which District has a Party of republican and a Result of lost re-election democratic gain?
SELECT "District" FROM table_37898 WHERE "Party" = 'republican' AND "Result" = 'lost re-election democratic gain'
SELECT "District" FROM "table_37898" WHERE "Party" = 'republican' AND "Result" = 'lost re-election democratic gain'