<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 72-year-old man presents to the primary care clinic for evaluation of progressive fatigue and weight loss. His past medical history is significant for hypercholesterolemia, type 2 diabetes mellitus, aortic stenosis, and chronic renal insufficiency. He endorses being well-rested after waking from sleep but fatiguing rapidly during the day. In addition, he states that he has lost 15lbs over the previous month. His temperature is 98.3F 36.8C, pulse is 100min, blood pressure is 11085 mmHg, respirations are 16min, and oxygen saturation is 96 on room air. Physical exam is notable for conjunctival pallor and scattered areas of ecchymoses. His laboratory results are shown below:Serum:Na: 140 mEqLK: 4.0 mEqLCl-: 101 mEqLHCO3-: 22 mEqLBUN: 30 mgdLGlucose: 160 mgdLCreatinine: 1.9 mgdLLeukocyte count: 1,100mm3Absolute neutrophil count 920mm3Hemoglobin 8.4 gdLPlatelet count: 45,000mm3Mean corpuscular hemoglobin concentration: 34Red blood cell distribution width: 12.0Mean corpuscular volume: 92 μm3Lactate dehydrogenase: 456 IULHaptoglobin 120 mgdLFibrinogen 214 mgdLA bone marrow biopsy is performed which shows cells that are CD19, CD20, CD11c, and stain with acid phosphatase 5 and tartrate-resistant. Which of the following is the next best step in the treatment of his disorder?? A: Hydroxyurea, B: Cladribine, C: Filgrastim, D: Doxorubicin, E: Cyclophosphamide,  <response>: Based on the information provided in the question stem, this patient has signs and symptoms of fatigue, weight loss, easy bruising, anemia, thrombocytopenia, and leukopenia. The bone marrow biopsy shows findings consistent with hairy cell leukemia. The choices provided are different chemotherapy agents. Hydroxyurea is not typically used as first-line therapy for hairy cell leukemia. Cladribine is a purine analog that is considered first-line therapy for hairy cell leukemia and leads to high response rates. Filgrastim is a granulocyte colony stimulating factor that would not treat the underlying hairy cell leukemia. Doxorubicin may be used but is not considered first-line. Cyclophosphamide is an alkylating agent that may be used but is not considered first-line.Therefore, based on the information provided, the next best step would be to treat with cladribine as it is considered first-line therapy for hairy cell leukemia.B: Cladribine 