Cancer and cancer treatment can sometimes interfere with male fertility. There are many things that come together and work properly for a person to have optimum fertility. Cancer in any of the tissues relating to reproduction can cause infertility. Cancer treatment can also have side effects that can cause infertility.

• Cancer that blocks or impresses on an organ is essential for reproduction.
• Cancer or cancer treatment interferes with the release of hormones that are
  necessary for conception.
• Cancer or its treatment may cause the impaired sperm production in the testicles.
• Blockage of sperm from ejaculation.

• Surgery
  Surgery may be needed for cancer in areas like the testes, penis, prostate, rectum or bladder. Surgery on the nervous system, brain or spinal cord may also require surgery if they are impacted by cancer. These surgeries can cause infertility in men.
• Radiation therapy
  Radiation therapy is often used by itself or in conjunction with surgery or medications to treat cancer. Radiation that is given to parts like the pelvis or testicles can damageth e sperm and cause infertility. A man can still be fertile during the radiation therapy, but the sperms may have incurred damages. If the partner gets pregnant during this time, she may miscarry or the child may be born with genetic disorders. To avoid this, your doctor will ask you to refrain from sexual activity during the treatment and for some time after it too.
• Chemotherapy
  Chemotherapy uses drugs to treat cancer, and it may cause the production of sperm to slow or stop. It will take years for the sperm production to go back to normal. In some cases, it may not happen at all.
• Immunotherapy
  Immunotherapy and targeted therapy work on cancer differently from the drugs of chemotherapy. Not much is known about how they affect fertility. The drugs are known to raise the chances of congenital disabilities in babies. So it is best not to try for conception when under treatment.
• Hormone therapy
  Hormone therapy can be used for treating cancer of the prostate, among other cancers. This can affect the number of sperm produced. The drugs used can also lower sex drive and cause erectile problems. These problems go away when the medications are stopped.
• Stem cell and bone marrow transplant
  High doses of chemotherapy and radiation are given to the body to transplant stem cells or bone marrow. This can permanently hamper a man’s capability to make sperms.

If you are diagnosed with cancer, and the doctor informs you that loss of fertility can be a possible side-effect, you can choose cryopreservation to preserve fertility. The sperm can be deposited conventionally or be retrieved from the testes or epididymis and be saved in a sperm bank. The sperm can be later used to impregnate your partner using ART treatment.