AZD2281 and Irinotecan in Treating Patients With Locally Advanced or Metastatic Colorectal Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed colorectal cancer * Locally advanced and/or metastatic disease * Disease considered incurable * Suitable for treatment with single agent irinotecan hydrochloride as a palliative intervention, as determined by the investigator * Must have clinically and/or radiologically documented disease * Patients whose only evidence of disease progression is tumor marker elevation are not eligible * Must have received no more than one prior oxaliplatin- and/or irinotecan hydrochloride-based chemotherapy regimen given either with adjuvant, neoadjuvant, or palliative intent * One additional adjuvant fluoropyrimidine (fluorouracil or capecitabine) regimen may have been given for relapsed or metastatic disease * No untreated brain or meningeal metastases (CT scan required if there is a clinical suspicion of CNS disease) PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Absolute granulocyte count ≥ 1,500/mm³ * Platelet count ≥ 100,000/mm³ * Bilirubin ≤ 1.5 times upper limit of normal (ULN) * ALT and AST ≤ 2 times ULN (≤ 5 times ULN if liver metastasis is present) * Serum creatinine ≤ 1.5 x ULN OR creatinine clearance ≥ 50 mL/min * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 90 days after completion of study therapy * Must reside within a 1½ hour drive from participating center * No other invasive malignancies, unless curatively treated with no evidence of disease * No GI tract disease resulting in an inability to absorb oral medication, including the following: * Uncontrolled inflammatory GI disease (e.g., Crohn's disease or ulcerative colitis) * Post-surgical malabsorption characterized by uncontrolled diarrhea that results in weight loss and vitamin deficiency or requires IV hyperalimentation * Pancreatic enzyme supplementation is allowed * No untreated and/or uncontrolled hypertension, cardiovascular conditions, and/or symptomatic cardiac dysfunction * No active or uncontrolled infections * No serious illnesses or medical conditions that would preclude study participation * No known hypersensitivity to the study drugs or their components, atropine, or loperamide * Not known to be homozygous for the UGT1A1\*28 allele * No known deficiency in glucuronidation of bilirubin, such as Gilbert's syndrome * No neuropathy ≥ grade 2 * Patients with persistent, stable, grade 3 sensory neuropathy, who meet other eligibility criteria may be allowed at the discretion of the investigator PRIOR CONCURRENT THERAPY: * Recovered from all prior therapy * No prior PARP inhibitor * No prior radical pelvic irradiation * No prior radiotherapy to ≥ 25% of bone marrow stores * Prior irinotecan hydrochloride allowed provided the drug was not discontinued due to toxic effects and the patient did not have severe irinotecan hydrochloride-related toxicity (grade 4 or requiring hospitalization) * At least 21 days since prior radiotherapy (exceptions may be made for low-dose, nonmyelosuppressive radiotherapy) * At least 30 days since prior chemotherapy * At least 21 days since prior hormonal, immunologic, biologic, or signal transduction inhibitor therapies * More than 3 weeks since prior and no other concurrent investigational drugs or anticancer therapy * At least 14 days since prior major surgery * Wound healing must have occurred * At least 14 days since prior and no concurrent CYP3A4 enzyme-inducing or -inhibiting drugs, including enzyme-inducing anticonvulsants, rifampin, rifabutin, St. John's wort, atazanavir, or ketoconazole * Dexamethasone is allowed for antiemetic prophylaxis