Acquired severe aplastic anemia

It is not a cancer. NMDP states it plainly, and it is worth saying first, because almost everyone arriving from a search assumes otherwise and reads everything differently once they know. There is no tumour to remove, no chemotherapy aimed at killing it, and no staging.

What has happened is that the bone marrow — the spongy blood-making tissue inside bones — has too few blood-forming cells left, so all three kinds of blood cell run low at once. Too few red cells, too few neutrophils (the white cells that fight bacteria), too few platelets (the cells that stop bleeding).

“Severe” is a defined threshold rather than a description. It means the marrow is largely empty on a biopsy, together with at least two of: neutrophils under 0.5, platelets under 20, or reticulocytes — brand-new red cells — under 60. “Very severe” is the same disease with neutrophils under 0.2. Below that severe threshold is a distinct, less urgent group that this page’s treatment choices do not describe.

It is rare, and it does not arrive at one age. Incidence in Europe is around 2 to 3 per million people per year, with peaks in the teens and early twenties and again over 60. A page written for only one of those groups would miss the other.

In most acquired cases the immune system is attacking the marrow. The NHLBI puts it directly: the most common cause of the damage is the immune system destroying the blood-forming stem cells. That single idea explains why suppressing the immune system works at all, and why recovery means the marrow being allowed to restart rather than something being removed.

For most people no trigger is ever identified. The BSH guideline puts 70% to 80% of cases as idiopathic, meaning no cause found. That is worth stating outright, because people search hard for something they could have avoided.

Named non-immune causes exist — some medicines, including chemotherapy drugs, and exposure to certain toxins and chemicals — but they account for a minority.

Before treatment starts, teams look specifically for inherited bone marrow failure syndromes such as Fanconi anemia and the telomere disorders, which can present looking exactly like this. Missing one has two serious consequences: the conditioning chemotherapy used for a transplant can be severely toxic to someone with a DNA-repair disorder, and a family donor may turn out to carry the same inherited condition.

Three failures at once, because all blood cells come from the same place. Too few red cells brings fatigue and breathlessness. Too few neutrophils brings infections that will not clear. Too few platelets brings easy bruising and bleeding.

In severe disease the immediate danger is not the anemia. It is infection and bleeding, and that is what makes it urgent.

Before treatment takes effect, life is built around transfusions, preventive anti-infection medicines and prompt treatment of anything that starts. Blood is matched more carefully than usual to reduce the chance of the body making antibodies against transfused cells — which matters, because repeated transfusions can make a later transplant harder.

There is a longer-term risk to know about, and it belongs on the page as a risk accruing over years rather than a forecast. Some people’s disease evolves into a myelodysplastic neoplasm or acute myeloid leukemia after immunosuppression. Published estimates differ and the risk does not appear to plateau, so it is a reason for indefinite follow-up rather than a number to carry around.

There are two genuine first-line paths, not one path and a fallback. The BSH guideline names them in one sentence joined by “or”: immunosuppressive therapy with horse ATG, ciclosporin and eltrombopag, OR a transplant from a matched sibling donor. What decides between them is severity, age, and which donor is available — taken together.

Immunosuppression means horse ATG, an antibody preparation raised in horses that damps down the immune cells attacking the marrow, plus ciclosporin to keep the immune system suppressed. Eltrombopag, a tablet that stimulates blood-cell production, is now added from early in treatment.

The RACE trial, run across 24 sites in six European countries, is the evidence for adding it: overall response at six months was 68% with eltrombopag against 41% without, and the median time to a first response fell from 8.8 months to 3.0. Two-year survival was 90% against 85% — so the trial improved the rate, speed and depth of response, and did not demonstrably improve survival. That distinction is worth keeping.

A transplant replaces the marrow with a donor’s blood-forming cells. Bone marrow rather than blood is the guideline-preferred graft source in this disease specifically, with less graft-versus-host disease and lower mortality in a large comparison.

Practice differs sharply between children and adults, and this matters. A transplant from a matched sibling is recommended upfront in children. Adults over about 40 usually go to immunosuppression first. If immunosuppression fails, children commonly move to an alternative-donor transplant while adults often receive a second course of immunosuppression.

Diagnosis is a process of exclusion, which means waiting — marrow biopsy, blood films, flow cytometry, chromosome breakage testing, gene panels — all before treatment can start. That delay is thoroughness, not neglect, though it rarely feels like it.

ATG is given in hospital rather than taken at home, and it has early effects: fever, rash, rigors, blood pressure swings, fluid retention. Then, usually somewhere between day seven and day fourteen, serum sickness — joint pain, muscle pain, rash, fever. It is expected and it is managed. It is not a sign that treatment is failing.

The thing least often explained is how slow the response is. Someone told that immunosuppression works may then experience months of nothing changing and reasonably conclude it has not. Half of people in the RACE trial had not responded at three months even with eltrombopag, and without it the median wait was nearly nine months.

The middle of this illness — between diagnosis and response — is built around transfusions, infection precautions and monitoring, and it is the part usually missing from disease pages. Afterward comes long-term surveillance for PNH and for changes in the marrow.

Two people with the same diagnosis can be on completely different paths because of their age and which donor exists for them. It is worth knowing that before comparing yourself with someone whose route was never open to you.

This is one of the conditions where an unrelated donor is genuinely a first-line route rather than something reached after everything else has failed — and it is worth being precise about what that does and does not mean.

A matched brother or sister is the preferred donor when one exists, and supplied 294 of the 718 transplants recorded in the EBMT reporting region in 2024. An unrelated donor supplied 317 of them. A half-matched relative supplied 105, so the choice is not sibling-or-registry-or-nothing.

The counterweight belongs in the same breath, because it comes from the same sentence of the same survey: 622 people were treated with immunosuppression in that region and year. Immunosuppression is comparable in volume to transplantation, and it is an intended first-line treatment rather than what happens when a search fails.

The honest donor-recruitment argument here is about timing, and it is documented rather than rhetorical. NMDP’s recommended timing for a transplant consultation in severe aplastic anemia is at diagnosis, and its patient page says to see a transplant doctor right away. The upfront unrelated-donor route for younger people depends on a matched donor being available within about eight to twelve weeks. Someone who joins a registry after a diagnosis is already too late for that window — which is the whole reason a registry has to be deep before anyone needs it.