Systemic mastocytosis with associated clonal hematologic non-mast cell lineage disease

Know what doesn’t get a lot of play?  Systemic mastocytosis with associated clonal hematologic non-mast cell lineage disease (SM-AHNMD.)  I’m guessing it’s because of the name.  It is SM with another blood disease that does not involve mast cells.

In spite of there being less easily accessible information on it, it is the second most common type of SM.  In patients with advanced SM, up to 50% fall into this category.  The second hematologic disease is almost always a myeloid neoplasia (bone marrow cells growing out of control), but about 10% of cases are lymphoproliferative diseases (white blood cells growing out of control.) 

About 45% of the time, the AHNMD is another myeloproliferative neoplasm (SM-MPN), like primary myelofibrosis or essential thrombocythemia.  SM-MPN has a better life expectancy than other types of SM-AHNMD and on average live 2-3 times longer.  29% of cases demonstrate CMML (chronic myelomonocytic leukemia), 23% myelodysplastic syndrome (MDS), and 3% acute leukemia.  Generally MDS presents with refractory anemia and excess blasts.  This means that usually the anemia (low red blood cells) does not respond easily to treatment, and there are lots of immature white blood cells. 

Mast cells in SM-AHNMD are usually CKIT+, and cells associated with the other hematologic disorders may also be CKIT+.  People with SM-AHNMD have too many eosinophils (another type of white blood cell) about 34% of the time, but this doesn’t seem to affect prognosis at all.  Some combinations of mastocytosis and hematologic disease are more common than others; ASM-CMML is fairly common in this subgroup.  SM-AML also happens with some frequency.  In some types of hematologic disease, SM can often be missed (occult SM), affecting treatment and symptom profile. 

In all instances, both SM and the hematologic disease should be treated in the same way they would in the absence of the other.  Prognosis is very specific to both the stages of SM and the hematologic disease.  There have been several calls in the community to classify the more common pairings of SM and hematologic disease as individual entities, as grouping them together often provides irrelevant data.