This study is testing a new medicine called **iopofosine I 131** for certain blood cancers like B-cell malignancies and Waldenstrom Macroglobulinemia (WM). **B-cell malignancies** are diseases where certain white blood cells (B-cells) grow uncontrollably. The study is divided into two parts: **Part A** for different B-cell cancers and **Part B** for WM patients who have had at least two treatments before. **Iopofosine I 131** is a type of medicine that uses a special radioactive substance, **iodine-131 (I-131)**, which targets cancer cells. This study is for adults who have already tried other treatments. Participants might need to meet certain health criteria, like having a good performance status (ECOG 0-2) and specific blood counts.

• This study involves multiple visits and treatments for eligible patients.
• Participants must have tried previous treatments and meet certain health conditions.
• Treatment might have risks due to the radioactive nature of iopofosine I 131.