LP - Lumbar Puncture, also known as a Spinal Tap

A lumbar puncture is a procedure where a needle is inserted into the lower spine to provide access to the spinal fluid. For leukemia patients, this is used to collect spinal fluid to test for leukemia cells, and also for injecting chemotherapy drugs into the spinal fluid.

More information can be found here:

http://www.nlm.nih.gov/medlineplus/ency/imagepages/19078.htm