How is immunotherapy on lymph nodes monitored?

Someone I know has recently been diagnosed with stage 3 melanoma, she has the mole removed but the lymph node biopsy showed a small amount of cancer cells present, so she has been offered immunotherapy.

 

Can anyone tell me how progress is monitored for immunotherapy for cells in lymph nodes? Will they do a biopsy everytime she has the therapy? Will she have the therapy until they are not present and then it stops? 

 

Anyone with this particular experience I would love to hear from you please!!!! xx