A Study of Pemetrexed and Folic Acid Given Before Surgery (Neoadjuvant Treatment) to Patients With Rectal Cancer.

Inclusion Criteria: * no prior therapy for rectal cancer * pathological/ cytological diagnosis of adenocarcinoma of the rectum. Patients must have operable rectal cancer that is amenable to surgery. * adequate organ function * Eastern Cooperative Oncology Group (ECOG) Performance status 0 or 1 * signed informed consent * at least 18 years of age * surgically sterile, postmenopausal (women) or compliant with a medically approved contraceptive regimen during and for 6 months after the treatment. Exclusion Criteria: * concurrent administration of any other anti-tumor therapy * treatment within the last 30 days with a drug that has not received regulatory approval for any indication at the time of study entry * serious concomitant systemic disorders * previously completed or withdrawn from this study * pregnant or breast-feeding * second primary malignancy * history of significant neurological or mental disorder, including seizures or dementia * inability to interrupt aspirin or other nonsteroidal anto-inflammatory drugs (NSAIDs) * presence of clinically relevant third space fluid collections that cannot be controlled by drainage or other procedure prior to the study entry * inability or unwillingness to take folic acid, vitamin B12 or dexamethasone