A 32-year-old female is being treated with methotrexate for a recently diag-
nosed choriocarcinoma of the ovary, and presents with complaints of oral
mucosal ulcers. The patient recalls being advised not to take folate-containing
vitamins during therapy. An uncomplicated surgical exploration was per-
formed 5 weeks ago with removal of the affected ovary. The patient has been
taking methotrexate for 2 weeks and has never had any of the above symptoms
before. On examination, patient was afebrile and appeared ill. Several mucosal
ulcers were seen in her mouth. The patient also had some upper abdominal
tenderness. Her platelet count is decreased at 60,000/mm3 (normal 150,000 to
What is the most likely etiology of her symptoms?
What is the biochemical explanation of her symptoms?
What part of the cell cycle does methotrexate act on?