Well, when untreated, ET can progress to leukemia. That's why it's so important to protect our bone marrow by taking HU.

I hope your friend will seek a second opinion.

Research shows that rare cases of leukemia have been attributed to Hydroxyurea after 20 years of use. I don't remember the dosage of the drug that may cause this outcome.

I am in the process of appointments with my 2nd opinion doctor (at Mayo ) who has confirmed my suspicion that my Doctor #1 has given me questionable information. Doctor # 1 did not think bone marrow biopsy was necessary for diagnosis because I have tested positive for JAK2 gene mutation. But my 2nd opinion doctor pointed out that the lab report states that the JAK 2 positive result only attributes to a 7% chance that it is the cause of high platelets. Therefore Doctor #1 started treatment with hydroxyurea every other day even though the cause of my high platelets (450) is still unknown. Doctor #2 will do the bone marrow test next week and he left me on the drug saying it is a low dose and will be ok.

A 2nd opinion may clarify my diagnosis and has been very helpful.

Take care.