Yes! Treating anemia is like filling the gas tank in your car.  you help replace the gas. Depending on the kind of anemia, you take supplements or change your diet so you get more iron or vitamin b12.  you figure out why your gas tank was running low and fix the leak. Are you bleeding somewhere in your gut? Heavy periods? Chronic disease? Not eating well? But yes, you can refill your tank!
Most/Not all anemias. Anemia is defined as a hemoglobin (hb) level <12 g/dl in females and <14 g/dl in males, or as a hb level <12.5 g/dl in adults.   .Risk factors include extremes of age, female gender, lactation, and pregnancy. The most common cause internationally is iron deficiency but could be B12 deficit, cause by inflammation or chronic disease, renal disease, lack of production or destruction of rbcs.
How many of the people with anemia are treatable, and how many are just born that way and untreatable? 50%/50%?
Majority treatable. There are a lot of causes of anemia- the most common are perhaps blood loss, decrease production- due to iron deficiency, vitamin deficiency, anemia of chronic disease - these are treatable minority cases such as hereditary anemia- such as diamond blackfan syndrome, fanconi's anemia, cooley anemia-much harder to treat-supportive tx only and bone marrow transplant to treat if possible.
Is iron-deficient anemia curable or just treatable? Once a patient is diagnosed with it, can they be un-diagnosed? Can it go away for good? Yes or no?
Find the cause. Once the cause (heavy monthly loss, bleeding ulcer, cancer, ill-advised vegetarianism, hookworm, others) is identified and addressed, replacing the iron solves the problem.
Is angioimmunoblastic t-cell lymphoma still treatable if in the marrow, anemia, low platelets, swelling?
Yes. Chemotherapy goes throughout the body and can be used to treat widespread lymphoma.
T cell lymphoma. It is treatable but need careful supervision under the oncologist as chemo can be detrimental with low blood counts but sometimes that is the only way marrow can be cleared of lymphoma so lot of thinking needs to be done in selecting appropriate chemo for such patients.