[SkepticalDebunker (OP)]

My friend has a type of skin cancer, can't remember which, but I had a cut on my arm and he accidentally bumped/scraped his skin, including the area of skin cancer, across the cut. I'm worried that the cancer cells got inside of the cut and I'm going to develop skin cancer. I didn't sanitize the area until I got home since I didn't have any while I was out. My dad said you can't catch cancer but aren't cancer cells a lot like viruses? They're rogue cells that have the ability to hide from immune systems, multiply out of control and take over the body. So what happens if cancer cells from another person get inside another person's body? Wouldn't the cancer cells grow exponentially and try and take over my body?

I've been worrying about this like all week, I keep looking up stuff but I constantly find articles and studies that contradict each other so I don't know what to trust or believe regarding this. help?

[Kryptid]

No, your immune system will recognize the cells as not belonging to your body. Unless you have an impaired immune system, I wouldn't worry about it.

[Janus]

Just to build a bit on Kryptid's answer. Cancer is a aberrant growth of your own cells.  This is why your immune system can have trouble dealing with it.   But any cells from some other person will be recognized as being foreign and attacked. 
This becomes an issue with organ transplants.  You first need to screen for a donor that has a close enough tissue match to yours, and drugs to suppress your immune system are used to prevent your immune system from rejecting the new organ.

[Bored chemist]

Unless your friend happens to be your identical twin, you will be OK.

[Petrochemicals]

I seem to remember a news story about transplant patients developing secondary cancer from cancerous organs, but given that a donated organ and a cancer are both foreign dna  and powerful drugs are given to subdue the recipients immune system this is not surprising. Transplant victims have a far higher cancer risk in their own cells due to these drugs.

https://www.kidney.org.uk/cancer-after-kidney-transplantation

Are you on immune suppressants? If not then you are as likely to develop cancer now as you where before. There is a doctor on this forum somewhere.

[paul cotter]

Cancer genes are almost identical to those healthy genes of the afflicted individual where as genes of a donated organ will be significantly different. The difference required to establish a neoplasm can be very small: just switching of the p53 apoptosis gene alone can cause abnormal growth but i'm not sure if this on it's own can lead to a recognised cancer as I have said before this is really not my field.

[evan_au]

The difference required to establish a neoplasm can be very small: just switching of the p53 apoptosis gene alone can cause abnormal growth but i'm not sure if this on it's own can lead to a recognised cancer.

I am not a doctor at all, but once I did a rough count, and worked out that you probably need around half-a-dozen mutations to turn a cell cancerous. The list went something like this:
- Switch off p53 apoptosis (otherwise the cell will commit suicide on detecting non-repairable mutations)
- Damage one or more genes governing accurate copying/proofreading/repair of DNA on cell division
- Turn on genes which promote cell division (in adults, most cells don't divide very often)
- Turn on factors which promote growth of blood vessels (otherwise the cancer cannot grow beyond a small size)
- Turn off cell senescence/enable telomerase; the limited length of telomeres will normally stop a cell dividing more than about 70 times. This will stop a cancer growing to a large size.
-Turn on factors which promote migration through the body (a localised tumour is much less dangerous)

Note that some of these mutations may occur before you are conceived: BRCA1 is usually inherited from a parent; this gene assists in DNA repair. https://en.wikipedia.org/wiki/BRCA1
- Some of these mutations may occur before you are born. Most human cells cannot divide more than about 70 times; more than half of these divisions occur in going from an egg to birth. https://en.wikipedia.org/wiki/Hayflick_limit

Note that elephants have a lower-than-expected cancer rate (for their size), because they have 40 copies of p53 in their genome (compared to 2 for humans). Whales also have multiple tumour-suppressing genes. Maybe we need to introduce this for astronauts? https://en.wikipedia.org/wiki/Comparative_oncology#Large_mammals

My friend scraped his skin cancer into a cut on my arm. Will I get his cancer?

There are some transmissible cancers, but they tend to occur in highly inbred populations
- One is decimating Tasmanian Devils
- Others have been seen in domesticated dogs, lab hamsters, and clams
- There have been a few cases in humans - mostly affecting humans with impaired immune systems such as AIDS patients or transplant patients.
https://en.wikipedia.org/wiki/Clonally_transmissible_cancer

Humans are sufficiently diverse genetically that your body is likely to recognise any cells from another person as "foreign", and attack them
- Cuts are already a hive of activity for immune cells, as a cut is a primary source of infections.

[Zer0]

@OP

Generalized responses have been provided to your Cancerous Thread.

Still, you are Requested to Please visit your G.P./P.C.P for a further Detailed analysis.

ps - Wish you & your friend,
alot many Smiles & Good health.
(live long & prosper)