Risk for ovarian cancer in women that use this drug for weight loss is far less present than in women who used this drug as a fertility treatment.
It is believed that HCG has protective effect for breast cancer.
This substance is produced and secreted by certain types of cancer, that is why its measurement in blood is a marker for cancer presence (HCG is a tumor marker).
I don't know if it is a good idea to take HCG like weight loss therapy, since it isn't FDA approved and there have been some studies that have shown its ineffectiveness.

Some tumors secrete HCG. If a person has HCG in their blood and is not pregnant and has not been artificially supplying it, it is being produced by a tumor. When the tumor secretes HCG, the immune system is not very likely to attack it.

Injecting yourself with HCG may stop your immune system from attacking cancer cells already present in you body.

Many people have cancer cells but their immune systems are able to erradicate them. Cancerous tumors appear when the cancer cells outgrow the immune system's abillity to kill them.