RT-PCR is also used to assess the following molecular response to treatment, defined as the ratio of BCR-ABL1 to ABL1 transcripts (known as molecular response (MR)) and categories in different groups including complete cytogenetic remission (MR ≤ 1%), major molecular response (MMR) (MR ≤ 0.1%), deep molecular response (DMR) ( MR4 ≤ 0.01%), and molecularly undetectable leukemia MR4.5 ≤ 0.0032% [60, 164]. The gene discussed is ABL1; the disease is leukemia.