Blood stem cells from 56 pediatric cancer patients being stored in a long-term freezer at the Children’s Hospital Los Angeles for use in possible future treatments were destroyed when temperature sensors failed earlier this month.

The hospital also acknowledged they had sent the notification letters directly to patients, some of whom are children, instead of to the parents.

In a statement Wednesday, the hospital said the cells were collected for routine reasons, and none of the patients' health was put in jeopardy as a result of losing the material.

Stem cells are very young cells that can develop into other types of cells. Blood stem cells, in particular, develop into different types of blood cells.

But why are these cells frozen and stored for certain cancer patients?

Blood stem cells from pediatric cancer patients are most commonly collected when patients are undergoing treatment for certain types of cancer called solid tumors, said Dr. Ludovico Guarini, a pediatric hematologist and oncologist at the Maimonides Children’s Hospital in Brooklyn, New York. Guarini is not associated with Children's Hospital Los Angeles.

Solid tumors are any tumors that form a mass, such as brain or liver cancer, versus liquid tumors, like those of the blood or lymphatic system.

Preserving stem cells allows doctors to give higher doses of chemotherapy or radiation, which can be toxic to blood cells, Guarini told NBC News. After the treatment, re-injecting the stem cells allows patients to replenish the blood cells that were wiped out. Blood stem cells also can sometimes be used to replace damaged bone marrow.

Obtaining stem cells can be arduous. The cells are either taken from the bone marrow, which often requires anesthesia, or, if they are taken directly from the blood, the bone marrow must be stimulated to release the stem cells into circulation.

Because of this, some stem cells are often put aside and stored for possible future use, in case a patient's cancer returns.

“Whether the lost stem cells are replaceable depends on the circumstances," Guarini said. For some patients, they may just need to repeat the collection process. But for others, if the cancer returns and is aggressive, an outside donor may be needed.

Children's Hospital Los Angeles said in the statement that the freezer has been replaced and that the maintenance schedule and sensor monitoring systems have been upgraded.

They are also reviewing their notification process to help avoid sending information like this directly to pediatric patients in the future.

The hospital said that it will provide support to the families affected if further care is needed in the future.

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