The extraction and cryopreservation of ovarian tissue can be performed shortly before beginning the cytotoxic therapy. It may also be combined with other techniques such as the transposition of the ovaries. Currently, a combination with ovarian stimulation and cryopreservation of fertilised or unfertilised oocytes is being tested in the FertiPROTEKT network and has been successful so far.
In order to preserve the ovarian tissue, either the whole ovary is resected laparoscopically or about ½ of the ovarian cortex is retrieved from one ovary and prepared and preserved using cryoprotective agents. Recent findings suggest that it is beneficial to at least leave a residual ovary in place so as to enable an optimised homologous transplantation later.
If, after a sufficiently long relapse-free interval, the patient wishes to get pregnant but suffers from ovarian insufficiency, the tissue is usually transplanted orthotopically to the remaining ovary (Donnez et al. Lancet 2004, 364:1405-1410; Meirow et al. N Engl J Med 2005, 353:318-321) or heterotopically into a peritoneal pocket (Andersen et al. Hum Reprod 2008 Jul 3. Epub ahead of print).
It should be noted that international experience with the cryopreservation of ovarian tissue is still limited. However, the birth of 15 children and several more pregnancies indicate the very high potential of this technique (Donnez et al., Ann Med).
FertiPROTEKT normally favours the laparoscopic retrieval of only a part of the ovarian cortex. It is usually an outpatient procedure so that it does not cause a lot of stress to the patient. If complete functional loss of the ovaries is expected, e.g. when the pelvis has been irradiated or bone marrow transplanted, it may make sense to retrieve the whole ovary. Immediately after the intervention, the tissue is transferred to a tissue bank which carries out the preparation and cryopreservation following the recommendations and standards of FertiPROTEKT.
The cryopreservation of ovarian tissue is especially suitable for younger patients since their ovaries still contain a great number of oocytes, so the chances of successful transplantation are higher. The upper age limited is 35 years. If the ovarian reserve is still very high, the age limit may be raised on a case-by-case basis.
This method is also suitable if there is only about ½ week left until the beginning of the cytotoxic therapy, so that it is no longer possible to stimulate the ovaries and extract oocytes, which would take around 2 weeks.
Theoretically, there is a risk that malignant cells are transplanted along with the tissue, but this transplantation risk has not been confirmed in practice. However, the possibility of cryopreserving ovarian tissue of patients with leukemia or a borderline tumor of the ovary should be treated with great caution.
Before the tissue is re-transplanted, various tests to exclude micrometastasis are carried out. Attempts have also been made to perform xenologous transplantation, i.e. the transplantation of tissue into immunodeficient mice. In this method, it seems to be easier to evaluate the risk of re-metastasis in cases of high-risk transplantations, e.g. after leukemia.