Frozen ovarian tissue from leukemia patients collected prior to radiation or chemotherapy may harbor malignant cells that escape detection by normal microscopic screening, according to a new study by researchers in Belgium. It is unknown whether implanting such tissue causes a resurgence of disease, but tests in mice suggests that it could.
To date, 13 children have been born to mothers who have had frozen/thawed ovarian tissue implants after cancer treatment, most of them in Denmark. One woman has had two children after such implantation. None of the patients have had resurgence.
Currently, ovarian tissue is examined for malignant cells by microscope after removal, but the new study and several others indicate such screening may be insufficient, especially in patients with acute lymphoblastic leukemia (ALL).
In the latest study, published online ahead of print in Blood (DOI 10.1182/blood-2010-01-265751), Marie-Madeleine Dolmans, MD, Professor of Obstetrics and Gynecology at Catholic University of Louvain, in Brussels, used a more complex test called real-time quantitative polymerase chain reaction, or RT-qPCR. She and her colleagues examined tissue from 18 leukemia patients, and fully 70% of the samples tested positive for malignant cells, even though histological exams were negative. Six of the patients had chronic myelogenous leukemia (CML), and the rest had ALL.
Next, to test whether the cells could become reactivated, the researchers grafted ovarian tissue into 18 immunodeficient mice. Within six months, four of the animals with grafts from ALL patients had developed intraperitoneal leukemic masses.
“The implication of this study is that doctors should not reimplant cryopreserved ovarian tissue in ALL patients, and probably CML patients as well,” Dr. Dolmans said in an interview. “Further studies are needed in CML patients, where leukemic cells were identified in the frozen tissue but xenografts did not demonstrate development of leukemic masses.”
Although the number of patients was small, the team concluded that RT-qPCR can identify contamination by malignant cells missed by histological screening.
“Our study provides clear evidence that cancer cells in women with acute and chronic leukemias can contaminate the ovaries,” Dr. Dolmans said. “If this tissue is reimplanted in these women when they're ready to have children, there's a good possibility that the cancer will come back.”
The National Cancer Institute estimates that 71% of ALL patients and 10% of CML patients are under the age of 35.
Other researchers have reported similar results in small studies using other advanced screening applications, said Kutluk Oktay, MD, Professor of Obstetrics & Gynecology, Medicine, and Cell Biology & Anatomy and Director of the Division of Reproductive Medicine & Infertility and Institute for Fertility Preservation at Westchester Medical Center-New York Medical College.
Dr. Oktay, who was the first researcher to obtain a viable embryo in a leukemia patient after implanting cryopreserved ovarian tissue, he told OT that the findings extend those made in 2008 by Israeli researchers in a paper published in the 2008 (Meirow D et al: Hum Reprod 2008 23:1007-1013). In their study, they too found evidence of malignant cells in cryopreserved ovarian tissue from leukemia patients that had evaded standard laboratory detection. The big question is whether such cells can cause a resurgence of disease, Dr. Oktay said.
“This study suggests that ovarian tissue harvested from acute leukemia patients may harbor cancer cells and result in the reseeding of the disease. There have not been any reports of cancer resurgence after ovarian transplants, and since the initial three days after the transplant is the ‘bloodless’ period in humans, while neovasculogenesis is taking place, it remains to be seen what the actual clinical risk for these patients might be.”
But since research on in vitro maturation is ongoing, he said the new study should not discourage oncologists from referring young females with leukemia to fertility-preservation counseling.
Last January, scientists at the Laboratory of Reproductive Biology and The Fertility Clinic, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark, reported similar findings screening preserved ovarian tissue from leukemia patients using polymerase chain reaction (Rosendahl et al: Fertil Steril 2010 Epub Jan 23).
They discovered that tissue from six of eight patients had malignant cells that had been missed by histological screening. The team also concluded that implantation might be dangerous, and recommended against reimplantation in leukemia patients.
While some studies of cryopreserved ovarian tissue implanted into Hodgkin's lymphoma patients have indicated that transplantation is safe, malignant cells have been detected in the bloodstream of implanted leukemia patients, Dr. Dolmans noted.
“At this time, the risk in leukemia patients and the capacity of these cells to develop into tumors after transplantation is totally unknown. One could imagine that these leukemic cells, although present in the frozen ovarian tissue, die after transplantation, but our study indicates that this is may not be the case.”
Only patients with ALL and CML were examined in the study, and other leukemias may behave differently, she noted. Importantly, leukemia-invaded ovarian fragments showed almost no signs of follicular development, and destruction of healthy follicles may eliminate risk.
“In patients with ALL, we should not retransplant their tissue for the moment. We can still propose ovarian tissue cryopreservation because these patients are often young and by the time they will need their tissue, research might have found another way to restore their fertility—for example, ovarian tissue culture with follicle maturation or follicle isolation and transplantation,” she said.
“Due to the lack of time for ovarian stimulation, or because of their prepubertal age, ovarian tissue cryopreservation is often the only option we can offer these patients at this time. For them, follicle culture with in vitro maturation may be a solution. Another option could be grafting of isolated follicles, enzymatically purified from frozen-thawed ovarian tissue. Research in this exciting new field needs to continue in order to develop safe options for fertility preservation.”
Dr. Dolmans and her colleagues have been working on ovarian follicle isolation for several years, with the aim of transplanting only purified follicles. Preliminary results on transplantation of human isolated follicles into mice show these follicles grow and mature after five months. The next step, she said, is to develop an artificial ovary using isolated follicles embedded in a matrix.
OT Board Member Michael Caligiuri, MD: Study Makes Clear that Reimplantation Cannot Be Recommended in ALL Patients
Asked for his opinion for this article, leukemia and lymphoma expert Michael A. Caligiuri, MD, Director of Ohio State University Comprehensive Cancer Center and CEO of the James Cancer Hospital and Solove Institute, said that there are many questions that remain unanswered by research on cryopreserved ovarian tissue from such cancer patients.
“While the numbers of cases studied are small and the conditions are experimental, the data from the new paper makes clear that reimplantation of cryopreserved ovarian tissue cannot be recommended in ALL at this time,” he said.
The initial treatment paradigm for patients with chronic-phase CML continues to evolve toward exclusive use of targeted therapy with tyrosine kinase inhibitors in the majority of cases, he noted, so a prospective analysis of cryopreserved ovarian tissue for contamination by CML in patients undergoing such treatments should be performed in a large group of patients. Moreover, stable-phase CML patients should now more seriously consider the non-emergent options of in vitro fertilization, with embryo cryopreservation as well as mature oocyte cryopreservation, he said.