Infertility can be a severe issue for many cancer survivors. Both chemotherapy and radiotherapy treatments can result in impaired fertility. For patients who remain fertile after cancer treatment, future conception will carry a much higher risk of fetal and maternal complications.
Loss of fertility can be very distressing for many cancer survivors, and it is thus important to maintain a discussion with your healthcare team about the impact that cancer treatment may have on your fertility.
Though there have been many developments in the field of reproductive techniques for cancer survivors, it is still vital for health professionals to acknowledge and discuss the possible impact to the patient’s reproductive health before cancer treatment, especially for child and young adult patients. However, some studies have shown that only a small number of oncologists will discuss the effects of cancer treatments on fertility, and even fewer will refer patients of reproductive age for a fertility preservation consultation.  Often, doctors will not even consider future fertility issues when treating childhood cancer patients, which can be distressing when survivors reach an age where they are looking to conceive. If patients have not yet undergone puberty, some fertility clinics offer the option of freezing ovarian and testicular tissue to reimplant when patients are older. 
Infertility in women
For a woman to conceive a child, she requires sufficient ovarian function and a uterus able to accommodate and nurture a fetus. Cancer and related treatments can damage these, thus affecting the patient’s reproductive capacity.
Many cancer treatments will affect the ovaries, which are a necessary component of fertility. If the ovaries are damaged, there will be diminished fertility as well as risk of early menopause.
Factors that affect fertility in cancer survivors include chemotherapy and radiation. Most chemotherapy drugs cause damage to the eggs, leading to infertility. With radiation therapy, the ovaries will absorb radiation directed at the pelvis, causing damage to them. 
A treatment which can have very important impact on fertility is surgery. Typically, there are several surgical options for reproductive cancers, and these will all affect fertility differently. A hysterectomy is a complete removal of the uterus, which means the woman can no longer carry a child. Removal of the ovaries, or oophorectomy, affects a woman’s ability to get pregnant, as she will no longer have any eggs. However, depending on the stage and spread of the cancer, it is sometimes possible to save one ovary and preserve eggs. Keeping at least one ovary will also prevent menopause symptoms such as hot flashes and vaginal dryness. Any surgery that causes scarring in the fallopian tubes will inhibit a woman’s ability to become pregnant, as the eggs will no longer be able to travel through these tubes to meet the sperm and become fertilized. 
It is possible to remove eggs from the ovaries and freeze them until you decide to have a child. Other options include having infertility treatment after cancer, adopting, or using a donated egg or embryo to have a child (sometimes with the help of another woman to carry the pregnancy). 
For more information, see Pregnancy after cancer.
Infertility in men
As a consequence of an increasing prevalence of relationships between older men and younger women, one can never assume a man’s reproductive goals based on his age. Therefore, much like with female cancer patients, it’s important to discuss fertility preservation with men prior to initiation of cancer treatment, while emphasizing the safety and reliability of sperm cryopreservation. 
Cancer treatments will affect male fertility in different ways. Chemotherapy aims to kill cells in the body that replicate quickly, and as sperm cells divide quickly, they are an important target for chemo drugs. Following chemotherapy, depending on the extent of the damage, sperm production will slow down or even stop altogether – although in some cases, it can take up to 10 years for sperm production to resume. 
Radiation to the pelvis or reproductive organs can cause sterility and erectile dysfunction in men (see Impotence). In addition to this, certain types of cancer can affect fertility. Testicle removal surgery, or orchiectomy, may not entirely compromise fertility if one testicle is left behind to continue sperm production. In the case of a bilateral orchiectomy, it will not be possible for the patient to father any children unless he has banked sperm prior to the surgery.  Other surgeries, such as prostate or bladder removal, may interfere with erection or ejaculation, but will not affect sperm production.
Much like ovary preservation in women, sperm can be collected and frozen before starting cancer treatment in order to preserve fertility.
 Kort, J. D., Eisenberg, M. L., Millheiser, L. S., & Westphal, L. M. (2013). Fertility issues in cancer survivorship, CA: A Cancer Journal for Clinicians, 64(2), pp. 118-134. DOI: 10.3322/caac.21205