instruction: provide the number of patients whose primary disease is neoplasm of uncertain behavior of other lymphatic and hematopoietic tissues\bone marrow transplant and age is less than 20?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic WHERE demographic.diagnosis = "NEOPLASM OF UNCERTAIN BEHAVIOR OF OTHER LYMPHATIC AND HEMATOPOIETIC TISSUES\BONE MARROW TRANSPLANT" AND demographic.age < "20"