The question ought to be what are myelodysplastic syndromes (MDS), since this is a group of similar blood and bone marrow diseases that can be considered very severe in some cases, mild in others, and have a wide degree of difference with regard to treatment options and life expectancy.
One thing about all of them is true: A diagnosis of MDS is a diagnosis of cancer.
MDS is split into two general categories: primary (de novo) MDS and treatment-related MDS. Primary (de novo) MDS simply means that the diagnosis has no obvious or known cause, while treatment-related MDS means it has an obvious or likely cause.
Unfortunately, the medical community has not agreed upon a single classification system for MDS subtypes, so there are two. There is the World Health Organization (WHO) classification system, and there is the French, American, British (FAB) classification system. The latter is most likely to be seen in the States, and it includes five general subtypes:
There aren't too many signs or symptoms associated with MDS. Generally speaking, though, sometimes a patient may experience some fatigue or shortness of breath while engaging in some physical activity. This is being caused by anemia, or not having enough red blood cells—something that would be picked up during a routine CBC.
A finding of anemia does not however indicate MDS. Rather, what is causing the anemia must be determined, and if the answer isn’t in the blood, it can be found in the bone marrow.
Diagnosis is made if the hematologist finds one among the handful of factors listed at the Leukemia and Lymphoma Society.
Primary MDS has no known cause, as previously mentioned. Treatment-related MDS can generally be traced to something like chemotherapy or radiotherapy having been given some years previously for the treatment of another cancer.
This is why MDS is often referred to as secondary leukemia. It also used to be called pre-leukemia because a certain subset of patients will go from having MDS to having acute myeloid leukemia.
In terms of treatment options, there are several:
Finally, as a last resort, some MDS patients may be recommended to take part in a clinical trial.