This is a prospective pilot study, the primary aim of which is to determine whether the presence of 18F FLT imaging signal uptake abnormalities correlate with clinically validated evidence of hematopoietic malignant disease (e.g. MRD, molecular, flow or histology) after immunotherapy and other treatments.

This prospective trial is designed to evaluate whether investigational 18F FLT imaging can identify the burden of hematopoietic disease both subjectively (by pattern of hematopoiesis in medullary spaces) and objectively (by SUV determination).

Patients undergoing therapy for treatment of high-risk acute leukemia or myeloma will be eligible for this study. Patients may or may not have undergone myeloablative hematopoietic stem cell transplantation. Two cohorts will be accrued: patients with high risk acute leukemia and patients with myeloma. In each cohort, patients will be accrued under two arms: Arm A - patients receiving immunotherapy and Arm B - patients who are receiving standard therapy (not immunotherapy or bone marrow transplant). Therefore, the leukemia cohort will consist of patients accrued in Arm A-L (immunotherapy) or in Arm B-L (standard therapy), and the myeloma cohort will consist of patients accrued in Arm A-M (immunotherapy) or in Arm B-M (standard therapy). Because patients with high risk acute leukemia or myeloma have poor prognosis with high risk for relapse, novel ways to evaluate the success of therapies would be valuable. 18F FLT reveals hematopoietic cell proliferation and can identify residual leukemia disease. On this trial, patients will undergo 18F FLT imaging pre-therapy and during a follow-up visit post-therapy. Patients in both cohorts will be imaged (Termed baseline scan) within one week prior to receiving respective therapies (e.g. immunotherapy or standard therapy) and then imaged approximately 28 days (+/-3 days) after the therapy termed Follow-up scan. After treatment, weekly follow-ups will be conducted for these patients till the follow-up scan (28 days +/-3 days) and then the final follow-up will be conducted post-1-year (after the start of immunotherapy or standard therapy).

Inclusion Criteria:

1. Aged 4 to 80 years
2. Evidence of high-risk hematopoietic malignancy with relapsed/refractory disease: acute lymphocytic leukemia, Acute myeloid leukemia, Ambiguous lineage leukemia, myeloma
3. Karnofsky/Lansky score of ≥ 50
4. Agree to use contraceptive measures during study protocol participation (when age appropriate)
5. Patient or parent/guardian capable of providing informed consent.
6. Ability to undergo 18F FLT imaging without sedation
7. Bilirubin < 2.5 mg/dL, AST/ALT <5x upper limit of normal, Serum creatinine < 1.0 or 2x the upper limit of normal (whichever is higher)
8. Pulse oximetry of > 90% on room air
9. Ability to undergo 18F FLT imaging without sedation
10. Anticipated immunotherapy (Arm A to include patients who received immune therapy with co-enrollment on a separate protocol or other immunotherapy) and Arm B, those who received other non-immune therapies to treat their cancers (excludes HSCT but includes chemotherapy or non-HSCT radiotherapy).

Exclusion Criteria:

1. Patients with uncontrolled infections
2. Pregnancy or lactating
3. History of prior fluorothymidine allergy or intolerance.