A 76 year old man presents with tiredness and easy bruising. He is an ex-smoker with a previous history of thyroid cancer which was treated with radiotherapy 10 years ago. Initial blood tests demonstrate that his Haemoglobin is 78 g/L, Platelet Count is 104 x 109/L, Mean Cell Volume is 98fl (normal range, 80-100fl) and Bilirubin is 74 umol/L (normal less than 21 umol/L).
What is the most likely diagnosis?