Pemetrexed Disodium in Treating Patients With Recurrent or Persistent Low-Risk Gestational Trophoblastic Tumor After a Molar Pregnancy

DISEASE CHARACTERISTICS: * Diagnosis of low-risk post-molar gestational trophoblastic tumor, defined as 1 of the following: * Increasing human chorionic gonadotropin (hCG) levels on ≥ 3 consecutive measurements taken over ≥ a 2-week period * Less than 10% decrease of hCG levels on 4 measurements taken over ≥ a 3-week period * Persistent or recurrent disease * Histologically confirmed complete or partial mole on initial evacuation * Prior pregnancy ≤ 12 months ago * No histologically confirmed choriocarcinoma or placental site trophoblastic tumor on initial evacuation * Failed only 1 prior dactinomycin or methotrexate therapy (with or without leucovorin calcium) * WHO score 2-6 * No evidence of metastatic disease, except to the lung or vagina, on physical exam, chemistry, chest X-ray, and ultrasound * No liver, spleen, brain, kidney, or gastrointestinal tract metastases * No more than 8 metastatic lesions PATIENT CHARACTERISTICS: Age * Any age Performance status * GOG 0-1 Life expectancy * Not specified Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Granulocyte count ≥ 1,500/mm\^3 Hepatic * Bilirubin ≤ 1.5 times upper limit of normal (ULN) * SGOT ≤ 3 times ULN * Alkaline phosphatase ≤ 3 times ULN Renal * Creatinine ≤ 1.5 mg/dL * Creatinine clearance ≥ 45 mL/min Other * Not pregnant or nursing * Fertile patients must use effective contraception during and for 3 months after study participation * No signifi…