Any person receiving organic tissue from an external source, whether another person or an animal, such as pancreatic tissue from a pig, risks rejection of the transplant and complications due to incompatibility. The cells of our bodies all have a large number of proteins in and on their cell membranes (outer surface). One type of protein located on the outer surface of the cell membrane is called a major histocompatibility complex (MHC), the primary purpose of which is to identify the cell as part of us. Except in the case of identical siblings such as twins, MHCs are unique to an individual, just like fingerprints. This is the most significant cause of problems in transplants and are what causes organ rejection. All recipients have to take immune system suppressants to stop their immune systems attacking the foreign cells of the transplant.
If, prior to the operation, the replacement tissue or organ is not sufficiently assessed and determined to be cancer free, then that patient may also be at risk of developing cancer from the transplant. If the organ or tissue that is transplanted actually does contain cancer cells of some type, that risk is greatly increased, but is still not a certainty.
Whether a transplant recipient develops cancer because of cancer cells located within the transplanted tissue, for example bone, skin or muscle, or organ is primarily dependent on the type of cancer cells now in their body and the cancer fighting capabilities of their body's immune system. Unfortunately, because our immune systems automatically attack foreign tissue, recipients of transplants receive drugs to suppress their immune systems, reducing but not eliminating their ability to fight cancers introduced through transplants.
The likelihood of receiving organs or tissues in a legitimate transplant operation that may contain cancer cells should be minimal. When people needing a transplant operation are in situations where their priority or the availability of donor organs makes it unlikely for such an operation to occur, and they have the financial resources to obtain a less legitimate transplant, the likelihood such transplants contain cancer cells is considerably higher.
The types of cancers that are most dangerous are those called malignant, those that produce tumors that are likely to metastasize (spread). But even the most malignant, such as osteosarcomas, do not always metastasize. So it is not a forgone conclusion that someone receiving a transplant containing such will necessarily develop an untreatable, widespread cancer.
Even when it comes to legitimate transplant operations, we do hear of horror stories where profit margin incentives over-ride medical ethics and result in testing failures, so that medical suppliers supply organs or tissues that should not be used due to inherent cancers or diseases. Although this is typically far rarer than TV medical and crime programs may imply for sufficiently dramatic plot lines.
The most logical course for any person needing a transplant to save their life, whether they can obtain a legitimate one or are forced to source a black market transplant, is to get multiple verifications on the suitability of the transplant material. At least two independent validations for a legitimate transplant and three or four for an under the counter operation. If that operation is being provided in a foreign country, take an expert from your own country with you.