The incidence of major bleeding in patients who receive thrombolytic therapy has been reported at 3.6%, with gastrointestinal bleeding the most common site followed by vascular access bleeds.The most typical cause of gastrointestinal bleeding is peptic ulcer disease.In the literature, few reports of thrombolytic therapy reveal undiagnosed colonic carcinoma.An 82-year-old man presented an acute posteroinferior myocardial infarction; he denied no gastrointestinal symptoms before hospital admission.Tenecteplase IV was administered with an improved clinical condition and an electrocardiogram showed reperfusion criteria.Approximately ten hours later, he experienced hematochezia; blood tests were relevant due to a descent of hemoglobin.A colonoscopy with biopsy revealed adenocarcinoma in the ascending colon.After stabilization, right hemicolectomy confirmed the cecum's invasive adenocarcinoma (T4aN0M0, stage IIB).The tumor was successfully removed, and chemotherapy was initiated.Thrombolytic therapy makes occult bleeding from colonic cancers obvious.Awareness of this fact may lead to earlier diagnosis of colonic cancers in asymptomatic patients and an increased likelihood of survival.Patients who develop gastrointestinal bleeding after thrombolytic therapy should receive a complete workup of the gastrointestinal tract to exclude serious but potentially curable diseases.