This is a prospective, twin-center, cohort study in patients discharged from the hospital after major abdominal or pelvic cancer surgery for cancer. This study is designed to evaluate the adherence to extended deep vein thrombosis prophylaxis (DVT) with the direct oral anticoagulant apixaban on the background of historical data from the investigator's center on low-molecular-weight heparin (LMWH) substandard adherence in the same setting.

All guidelines have embraced the concept of extended DVT prophylaxis after major abdominal or pelvic surgery for cancer, but the recommendation is consistently to use LMWH, which is more complicated than orally available prophylaxis, more expensive and has poor adherence.

The patients will be identified in the pre-operative admission or in post-operative orders as potentially eligible for extended prophylaxis. On the day of discharge a research assistant or a research nurse will approach the patient, provide information about the study and obtain written consent if the patient fulfills the eligibility criteria.

Each patient will be asked to take apixaban until postop day 29±1 and will be followed until postop day 90±3. The total duration of the study from first patient in to last patient out is expected to take 12 months.

At 1 week after discharge there is a telephone contact to ask about any side effects from apixaban or bleeding events or signs of thromboembolism and to answer any questions from the patient.

At postoperative Day +28-30 there is a telephone contact to ask about side effects, bleeding, signs of venous thromboembolism (VTE), until what date the patient has taken apixaban and estimate of missed doses using a standardized script. If the patient is still taking it, instruction will be given to discontinue. Self-reported modified Morisky Medication Adherence scale with 6 statements will be used At 90 days ±3 days there is the last telephone contact to ask about bleeding events or signs of VTE. The study is complete for the patient. At the time of Visit 4 the pharmacy that the patient uses will be contacted to provide dispensing record for apixaban, in order to verify that the patient filled the prescription.

Inclusion Criteria:

• Patients of at least 18 years of age, discharged after hepato-biliary, colorectal or gynecology-oncology abdominal/pelvic surgery (laparoscopic or open) for cancer and considered at increased risk for VTE (e.g. previous history of VTE, residual cancer, slow mobilization, obesity, comorbidities).
• Written informed consent obtained.

Exclusion Criteria:

• Patient unable to take tablets, even if crushed.
• Active bleeding.
• Venous thromboembolism diagnosed during the hospitalization.
• Severe hepatic impairment (Child Pugh class C).
• Severe renal failure on dialysis or with calculated creatinine clearance <15 mL/min.
• Platelet count <50·109/L.
• Concomitant treatment with azole-antimycotics, e.g., ketoconazole, itraconazole, voriconazole, or posaconazole, and HIV protease inhibitors, e.g., ritonavir.

male, female, other