- CML is one the four major leukaemia that affect adults. Incidences and patients numbers diagnosed with these leukaemia every year in the United Kingdom (UK) are shown in Table 1.
Table 1 Main leukaemia and their incidences in the UK (2016-2018)1
| Leukaemia type in adults | Incidence per 100,000 people | No of UK patients affected per year |
| Acute lymphoblastic leukaemia (ALL) | 1.1 | 791 |
| Acute myeloid leukaemia (AML) | 4.9 | 3089 |
| Chronic lymphocytic leukaemia (CLL) | 6.2 | 3803 |
| Chronic myeloid leukaemia (CML) | 1.3 | 829 |
1 Cancer Research UK, https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/leukaemia-cml. Accessed: February 2022
- CML is a chronic myeloproliferative neoplasia (MPN).
- Excesses of red blood cells, white blood cells or platelets in the bone marrow are characteristic of MPN blood disorders.
- With MPNs, the myeloid stem cells in the bone marrow make too many cells that do not function properly (Swerdlow et al 2017).
- In a normal bone marrow, the myeloid stem cells give rise to immature myeloid cells. These cells become red blood cells, platelets or white blood cells of myeloid origin (granulocytes and monocytes) (Figure 1).
- Granulocytes include neutrophil, basophil and eosinophil white blood cells. Granulocytes have small granules within the body of the cytoplasm of their cell, hence their name of granulocytes. These granules contain proteins used for fighting off viruses and bacteria (De Kleer et al 2014).
- Monocytes give rise to macrophages and dendritic cells (De Kleer et al 2014). Monocytes, macrophages and dendritic cells remove the products of infection from the body (Hirayama et al 2017).
Figure 1 Development of stem cells in the bone marrow
Source: Leukaemia Care
- With CML, any blood cells of myeloid origin such as the stem cells or the immature myeloid cells may multiply excessively. Of the myeloid blood cells that may multiply excessively, the granulocytes are the most likely to do so.
- Because these leukaemia cells are not fully mature and cannot function properly, they are unable to fight infections. Moreover, they accumulate in the bone marrow and prevent it from producing healthy blood cells of all types.
- The incidence of CML is higher in males, with a male‑to‑female ratio of 1.6 to 1.
- Median age at diagnosis for CML patients is 50‑60 years of age, although it may occur at any age.
- It is rare in children and adolescents, with only 2.7% of CML cases being younger than 20 years of age.
- Patients with CML can present in one of three phases:
- Chronic phase: This is the most common phase in which CML patients present. They can remain in this phase for years before proceeding to the accelerated phase. The only haematological finding is an increase of identical (clonal) mature myeloid cells (Bonaficio et al 2019). Clonal means that all the cells are genetically identical and have a single common ancestor cell.
- Accelerated phase: In this phase, the number of leukaemia cells start to increase, and symptoms become apparent. The accelerated phase normally lasts between three to nine months.
- Blast phase: This final phase of CML is also called the ‘blast crisis’. In this phase, the leukaemia blast cells increase massively and patients experience more obvious symptoms. The term ‘blast’ just means immature, but has given its name to this phase of CML.
