PLE-2012

A 60-year-old male patient came in due to easy fatigability. No other symptoms were noted on review of systems. On examination, the patient was noted to be pale with no oral lesions or palpable cervical lymphadenopathies. Chest and abdominal physical examination findings were unremarkable. Digital rectal examination revealed a smooth rectal vault with no blood on the examining finger. Complete blood count revealed a hemoglobin level of 9.5g/dL. What is the most likely pathology?