The blood thinner "tinzaparin" might increase survival in patients with colon cancer undergoing surgical resection. The investigators want to assess if a trial allocating patients to prolonged treatment with tinzaparin versus standard of care is feasible.

Cancer patients are at high risk of postoperative thrombosis and this risk remains elevated beyond the period of hospitalization. Thromboprophylaxis effectively reduces the risk of post operative VTE in cancer patients. Extended thromboprophylaxis beyond hospitalization (up to 30 days) with LMWH has been shown to further reduce the risk of postoperative VTE. Concurrently, there is a growing body of evidence to suggest that LMWH may have anti-cancer effects due to anti-metastatic properties and may improve survival in cancer patients, even in the absence of a documented VTE. Retrospective studies have shown that perioperative thromboprophylaxis (i.e., starting thromboprophylaxis before the surgery) seems to increase survival in cancer patients undergoing abdominal or pelvic cancer surgery with curative intent. The investigators propose to perform an open-label RCT to determine if thromboprophylaxis using tinzaparin 4,500 IU daily, starting from the time of decision to operate through the peri-operative period and extending for 4 weeks postoperatively, is feasible.

Inclusion Criteria:

• Males or females aged 18 years or older with a pathologically confirmed localized invasive colorectal cancer and no evidence of metastatic disease who are scheduled to undergo surgical resection will be eligible.

• All study patients must be enrolled at least two weeks prior to scheduled surgery and provide written informed consent.

• All the following criteria must be met to be eligible:

  1. Pathological confirmation of an invasive adenocarcinoma of the colon;
  2. No evidence of metastatic disease by Computed Tomography (CT) scan of the abdomen and pelvis or chest X-ray (CXR). A Magnetic Resonance Imaging (MRI) of the abdomen and pelvis will be used if the patient has a documented contrast allergy or to verify a questionable finding on the CT scan. Any abnormal findings on CXR will be investigated with a CT scan of the chest. Imaging must be performed within 2 months of randomization;
  3. a scheduled surgical operation for resection of the colon cancer; and
  4. ECOG performance status 0 or 1.

Exclusion Criteria:

• Subjects cannot be included in this study if any of the following criteria apply:

  1. rectal adenocarcinoma (defined as tumor below the peritoneal reflection or within 12 cm of the anal verge by rigid sigmoidoscopy);
  2. prior VTE including deep vein thrombosis (DVT) or pulmonary embolism (PE);
  3. requirement for full dose perioperative anticoagulation;
  4. requirement for anti-platelet or anti-inflammatory therapy that cannot be discontinued;
  5. contraindication to heparin therapy **;
  6. geographic inaccessibility (less likely to comply with required follow-up visits and care);
  7. participating in another interventional trial that may result in co-intervention or contamination (to be determined by PI);
  8. < 18 years of age;
  9. history of other malignancies (except for adequately treated basal or squamous cell carcinoma or carcinoma in situ) within 5 years of the colorectal cancer diagnosis;
  10. treatment, including radiation therapy, chemotherapy or targeted therapy, administered for the currently diagnosed colon cancer prior to randomization;
  11. pregnant or lactating; and
  12. unable/unwilling to providing informed consent.