How rare is burkitt's lymphoma?

Uncommon. Burkitt's lymphoma comprises about a third of childhood lymphomas, but less than 1% of adult lymphomas in europe and the usa. This very aggressive malignancy is much more common in africa, however.
Quite rare. It is a b-cell undifferentiated lymphoma, associated with ebstein barr virus, highly treateable and curable with chemotherapy and sometimes radiotherpay.