Answer:
A necessary but not sufficient cause
Explanation:
A necessary but not sufficient cause is defined as any cause/condition that is an obligate requirement for a particular event to occur (in this case, the particular event is leukemia disease), but it isn't sufficient for the occurrence of this event. Conversely, a sufficient cause is defined as any cause/condition that will cause by itself the event to occur. Finally, a condition is neither necessary nor sufficient when the condition neither is required nor sufficient for the event to occur.
