B-cell acute lymphoblastic leukemia (B-ALL)

A lymphoblast is an immature cell in the bone marrow that should grow up into a B lymphocyte — one of the white blood cells that fight infection. In B-ALL those cells stop maturing and multiply instead, filling the marrow with cells that will never do the job they were made for.

“Acute” means it develops over weeks rather than years, which is why treatment usually starts within days of diagnosis. It describes the pace, not the outlook.

You will hear several names for the same disease. Pathologists write “B-lymphoblastic leukemia/lymphoma”, which is the formal WHO classification. Families are told “ALL”, “pre-B ALL”, or “B-cell precursor ALL”. There is also a second lineage, T-cell ALL, which is a genuinely different disease with a different treatment conversation.

Doctors do not treat B-ALL as one thing. It is sorted into risk groups using age, the white cell count at diagnosis, genetic changes in the leukemia cells, and how quickly the leukemia clears — measured as MRD, the tiny amount left after the first round of treatment, found by tests far more sensitive than a microscope. That risk group drives everything that follows, including whether a donor is ever needed.

In most cases nobody knows. The NCI says it plainly: the exact cause of the cell changes behind childhood ALL is often unknown. Most children who develop it have no identified risk factor at all.

Some inherited conditions do raise the risk — Down syndrome, neurofibromatosis type 1, Bloom syndrome, Fanconi anemia, ataxia-telangiectasia, Li-Fraumeni syndrome and constitutional mismatch repair deficiency among them — as do exposure to radiation, including x-rays before birth, and previous chemotherapy. Those account for a small minority of cases.

The leukemia itself comes from genetic changes acquired inside the blood-forming cells, after birth. Having a risk factor is not the same as having a cause, and the NCI is explicit that ALL develops in many children with no known risk factor and does not develop in most children who have one.

It is a cancer, which means it cannot be caught from anyone or passed to anyone. Nothing a parent did or did not do caused it.

The marrow fills with lymphoblasts and stops making enough of everything else. Almost everything a person notices comes from that shortage rather than from the leukemia cells themselves.

Too few red cells brings tiredness, weakness, pale skin and breathlessness. Too few platelets — the cells that stop bleeding — brings easy bruising, bleeding gums, nosebleeds, and pinprick red spots on the skin. Too few working white cells brings fevers, and infections that arrive often or hit unusually hard.

In children the NCI also lists bone or joint pain, swollen glands in the neck, armpit or groin, and loss of appetite. Bone pain in a child is very often put down to growing pains or a sports injury before anyone thinks of leukemia.

Because it moves fast, the gap between “something is not right” and a diagnosis is usually short — days to a few weeks. Diagnosis involves a blood count, a marrow sample taken from the hip bone, and a lumbar puncture to check the fluid around the spinal cord, because B-ALL can reach the brain and spinal cord.

The main treatment is chemotherapy given in phases over years, and most children are cured without ever needing a donor. The phases have names families quickly learn: induction, which clears the visible leukemia; consolidation or intensification, which goes after what is left; and maintenance, a long stretch of low-intensity treatment to stop it returning.

The length surprises almost everyone. The NCI puts average adult treatment at one and a half to three years. For children, Cancer Research UK describes maintenance alone lasting about two years from the start of consolidation, with clinic follow-up continuing at least five years after treatment ends.

Maintenance is mostly taken at home — a daily mercaptopurine tablet at the same time each day, weekly methotrexate, periodic vincristine injections, short steroid courses and lumbar-puncture chemotherapy. Many children are back at school and playing normally while it runs.

Some B-ALL carries the Philadelphia chromosome, a swap between two chromosomes that creates an abnormal growth signal. That subtype is treated with a daily targeted tablet called a tyrosine kinase inhibitor added to chemotherapy, and the NCI reports long-term survival now routinely seen with that combination.

For relapsed or resistant disease in adults there are antibody-based drugs — blinatumomab, which brings a person’s own T cells onto the leukemia, and inotuzumab ozogamicin, an antibody carrying a chemotherapy payload. There is also CAR-T, and it is worth being precise about what CAR-T is: the patient’s own T cells are collected, re-engineered in a laboratory and given back. No donor is involved at any point. It is approved only for disease that has relapsed or not responded — tisagenlecleucel through age 25, and brexucabtagene autoleucel for adults since 2021.

The start is abrupt. Diagnosis to first chemotherapy is usually a matter of days, and families describe losing an ordinary life inside a week. Induction generally means several weeks in hospital — Cancer Research UK puts it at about four to eight weeks for adults, mostly as an inpatient.

A central line goes in early and stays for months or years, because there will be a great deal of infusing and a great deal of blood taken. Lumbar punctures recur through every phase, usually under sedation for children.

Steroids are a large part of ALL treatment and are a burden of their own kind. They bring mood and behaviour changes, a ravenous appetite and sleeplessness, and parents very often name steroid weeks as the hardest part of the whole thing — harder than the chemotherapy.

Then comes the part nobody is prepared for: maintenance. Roughly two more years of daily tablets at home, weekly doses, regular blood tests and clinic visits, during which the child looks well and the family looks recovered from the outside while treatment is still running every single day. Long stretches of low immunity mean a fever is not a minor event — it is an unscheduled hospital admission.

For the minority who go to transplant, treatment becomes shorter but far more intensive, and maintenance is not given. For those who receive CAR-T the short-term toxicity can be substantial, and it is managed in hospital.

For most children with B-ALL, a donor plays no part at all. Standard chemotherapy cures the majority, and the 2025 EBMT recommendations mark allogeneic transplant as generally not recommended for children at low risk in a first remission.

But for a defined minority, an unrelated donor is not a fallback. It is the standard route. EBMT rates transplant from a matched sibling and from a well-matched unrelated donor identically — both standard of care — for high-risk children in first remission, and for anyone in a second remission or beyond. In adults the same rating applies to Philadelphia-positive B-ALL in first remission, to Philadelphia-negative high-risk first remission, and to second remission.

That equivalence is the thing worth carrying away. Only about a quarter to a third of people have a matched sibling. For everyone else in that group, a well-matched stranger is not second best — it is the same standard of care, and it depends on someone having joined a registry.