Differential Diagnoses

A 55 year-old male presented to the clinic complaining of fatigue since two months ago. The fatigue is not relived by rest and is worse with exertion. Also he complains of exertional palpitations, somnolence that has being getting worse. Other complaints are intermittent painless rectal bleeding after bowel movements. Denied diarrhea, constipation, nausea, vomiting. Physical examination normal except pale conjunctiva and tachycardia.
Introduction
Should be a paragraph that provides a brief overview of the case and main diagnosis:

1-Adenocarcinoma of the Colon
:

                                     Differential Diagnoses

Differential Diagnosis:
Provide EACH differential diagnosis with the rationale and supporting evidence with the REFERENCE for each one. Also explain why differentials (2&3) were not the primary diagnosis.
1- Adenocarcinoma of the colon
2- Iron deficiency anemia
3- Colon polyps