What is a "Line" of Therapy in Multiple Myeloma?

But with myeloma therapy typically given in combinations, what does a "line" include? It was confusing even for myeloma experts like Vincent Rajkumar, MD (Mayo Clinic), Paul Richardson, MD (Dana Farber Cancer Institute) and Jesus San Miguel, MD, PhD (University of Navarra, Spain) better to define the criteria in an article published by the American Society of Hematology. 

What is a "single line" of therapy?

One line of therapy consists of any of the following:

1. One complete cycle of a single drug
2. A combination of several drugs (for example Revlimid/Velcade/dex)
3. A planned sequence of therapies (for example 6 cycles of induction therapy with Revlimid/Velcade/dex, a stem cell transplant and lenolidomide maintenance)

Seems like a lot of therapy for one line, right? But it's still considered one line of therapy.

What is a "new line" of therapy?

A new line of therapy would be considered:

1. Starting a new combination or myeloma treatment if you have stopped all drugs in the prior line of treatment.
2. The unplanned addition or substitution of one or more drugs in the existing regimen. For example, if you were on a triple combination and the lenalidomide portion stopped working and you started on pomalidomide instead, this would be considered a new line of therapy. 
3. An additional stem cell transplant if the second transplant was not part of a tandem transplant plan.
4. If a regimen is interrupted or discontinued for any reason, and then restarted at a later time point but one or more other regimens were administered in between, or the regimen is modified through the addition of one or more agents, then it should be counted as two lines.