**3.4 Molecular biology**

The most modern and effective methods for detecting BCR-ABL transcripts are based on molecular biology techniques. Polymerase chain reaction (PCR) testing of peripheral blood RNA is highly sensitive: it can detect 1 Ph-positive cell expressing the BCR-ABL fusion transcript in 105 –106 normal cells [1].

Real-time PCR is a great ally of clinical oncologist seeking better therapeutic outcomes because it helps in defining treatment, which can be more or less aggressive according to each patient's response [41]. Importantly, molecular methods, although extremely sensitive, do not allow observation of concomitant gene or chromosomal alterations.
