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I am NOT a vet, I am not an animal researcher. I am a loving rat mom and responsible breeder who has researched these health issues. I encourage everyone to always research yourself, consult your vet and use your instinct to decide what is best.

If any breeder tells you their lines are 100% won’t/can’t develop tumors they are either lying, scamming you or sadly just do not understand how those health issues work.

Every breeder would LOVE to be able to say that but rats are very prone to these issues and yes good breeding/genes play a huge role in a rats health but the main importance is their home care and environment. Good breeding will help rats be more resistant and better suited to fight off health issues but it does not make them immune.

I will always be open and honest about any health issues in my lines.

Sadly tumors are fairly common in rats, mostly females (but males can get them as well). The info I found says that in lab studies (nothing very recent but mostly from the 80s-90s) 17% to 75% for mammary tumors, and from 39% to 66% for pituitary tumors*(see link below). That is a fairly wide window for one. And it is fair to say that lab rats are far different from our own pets. There is really no way to tell how many pet rats get tumors as there is just no way to properly track it.

The two most common types of tumors in rats are Mammary & Pituitary Tumors.

Mammary tumors are mostly found in female rats in the arm pit, abdomen or groin. The tumors by far are mostly benign but they can cause discomfort, pain, lessen mobility- which can cause the rat not to be able to properly groom itself or eat/drink, it will cause weight loss, harm the organs. These tumors also can cause some serious painful health issues and death.

It is very important to catch them early and in most cases have them removed through surgery. Sadly they often do return though.

Sadly I see alot of pet owners shrug it off and let their rat suffer with a tumor until it grows to an insane size, they dismiss it as not being a big deal since it is benign and isn't in the way/isn't bothering the rat.

That is 100% BS & not true. I am not sure if they just want to believe that to make themselves feel better or what. But the tumor plays havoc on a rats body. Even if the rat seems fine, the tumor is draining resources from the body, causing stress and pain. They ARE suffering. The most humane thing is to have it removed asap or humanely euthanize the rat so it is not suffering.

Pituitary tumors are found in the pituitary gland of the brain that regulates hormones. These are mostly benign and usually appear in older female rats. These tumors play havoc on the rat causing many health problems including; weakness, mobility issues, stumbling, difficulty holding food and/or eating, loss of balance, head tilt/bumping/pressing, blindness, behavioral changes, weight loss, dehydration, etc…

It is a very serious condition and euthanasia should often be considered.  

Why Good Breeding Matters?

Many scientists have done cancer studies using rats as the characteristics of the tumors/cancer between us and them are so similar. So we do have some information and studies out there.

We all know now the genetic link of breast cancer in humans. Women should all be aware and cautious if we have a family history of it. It is the same with rats.

Studies have shown that there is not a simply yes/no of will you get cancer or not. Instead there are genes that are sensitive and resistant. So some rats may be at a higher risk than others.

Good breeders will not breed rats that have shown they are prone to health issues or tumors. If a rat develops tumors it is a good idea to end that line period. Ideally a line will be long and established and tumor free. Breeders should hold back some rats until a natural death to watch for tumors and should hopefully get feedback from adopters on if any of their rats have developed tumors.

It is not so cute and dry though. Even rats with the sensitive genes may never develop tumors if they are very well cared for and not exposed to carcinogens, a healthy weight, fed a healthy diet, kept in a healthy nonstressful environment.
At the same time rats who have resistant genes may still get tumors if exposed to these issues.

So as a breeder if none of my kept rats ever develop a tumor, there may be luck and very good care involved. And if an adopter does have a rat develop a tumor it could be care/environmental.

So we really need to look at the big picture and keep track of how many rats and why.

Still good breeding and established lines where we can see a history of the health of the line helps alot!

Prevention: What you can do at home?

By far the most important thing for healthy tumor free rats has been shown to be a healthy diet. I can not stress this enough!

  1. Keeping your rats a healthy weight.
    Obese animals are not cute, they are unhealthy walking time bombs. It will not only kill them, & shorten their lifespan but it will also make their last months with us painful. I often hear people say “oh so what, spoil them they have short life's anyways” but it does matter what kind of short life we are giving them. I want them to have the longest life possible and a quick peaceful death. Health problems come with pain and discomfort. Not being able to move or get around easily is not fun for them. Joint pain and an increased risk of bumble foot. And as stated above tumors are painful and not a good way for them to spend their last moments.

    You can still make your rats spoiled and well loved without fattening them up! Rats will be just as happy getting a veggie treat as a piece of cake. Find yummy healthy treats! Remember moderation.


  2. Diets should be low calorie and low fat. Pay strong attention to sugars as well!

  3. Watch for food sources that contain known carcinogens (substances capable of causing cancer). Many preservatives/dyes are known for this. You will not believe how many pet foods out there contain them! BHA, BHT, Ethoxyquin, and Red Dye#40 (which caused cancer in rodent studies!)
    The FDA says these are known to cause cancer & suggest we have limited amounts. So even if you want to dismiss them as ok in moderation, being part of their main daily diet is still dangerous IMO.


  4. Buy good brand foods! Cheap foods are so bad. They often have loads of sugar, one brand of Kaytee had three different sugar sources in it! This is to make it sweet and nummy for the rats to eat it. All those sugars make for fat (also diabetes prone) rats! They almost always contain dangerous preservatives and often contain dyes. Any pet food that contains dyes is to make us feel it is “fun”, the animal does not care and it is usually dangerous. This is why I also stay away from treats designed for pets!


I hate corn in pet foods. It is cheap filler. People often think of corn as a veggie so it’s healthy! But really corn is more so a grain and grains = carbs/sugar. Corn has a fairly high glycemic index, they warn diabetics to avoid or only in moderation. Hence why we create High Fructose Corn Sugar from… corn. Diets high in corn can lead to weight problems. Also it truly is a filler, it is not bringing healthy nutritional value to the food. It is like when we buy a bag of chips and it is 75% air, except the air at least helps the chips not get smashed up! Corn is also very often a GMO food, is that bad or good? That is for you to decide.


Feed a healthy diet! Give them a good healthy well balanced block diet and on top of that give them lots of fresh non processed foods. A bite of this or that is fine, moderation is key. I have been known to bribe mine with a cheeto or two shhh! But remember it is very easy to go overboard. Rats are very itty bitty, a tiny bite can play a major role in their diet/health.


Catching things early is important.
Do health checks often on your rats. Look them over, hold them and see if there is any strange issues popping up.

Weigh your rats and look for signs for weight loss.
Monitor their health, behavior, etc…

Make sure that it is infact a tumor and not an abscess.
Consult your vet right away if you have concerns.



Spaying has been shown to significantly reduce the chance of tumors and tumors from returning.


That being said spaying can be a bit controversial. In the pet world there has definitely a weighing concern on the positive and negative effects of spaying/neutering our pets. It does have ramifications throughout the entire body with a big change such as that. I think that is for each person to consider and decide.

But for spaying rats there is a real risk during the surgery. Rats are very small and need a well experienced vet. Being so small there is also added risk from the anesthesia. We also issues in recovering when you have a small flexible animal that may not properly rest or chew/lick at the surgery site.


While I believe the overall consensus in the rat community is that it is best to only spay rats that have had tumors. So you take the rat in to have the tumor removed and spayed. Having a tumor shows she is prone to it and it is likely they will return.


Besides that I would discuss the issue with your vet and weigh the pros/cons and decide for yourself.

My opinion is not to put a rat through the risk of surgery unless they are young and otherwise healthy & have a tumor.



The itty bitty cuties have a very special quality about them… they are far less prone to tumors!

Dwarf rats were first created in labs working on cancer research. They bred dwarfs that had a Growth Hormone Deficient. What that means is that with less growth hormone (which helps make them smaller) they are also less prone to tumors.

Yes it is awesome!

They are not immune to tumors but they are less prone.

The health of my lines:


As I have said, I will not breed sick animals. I will not breed a line that is prone to tumors.
My rats get fed a very healthy diet and not a single rat is overweight.
I keep lots of my bred rats as pets and breeders and monitor the health of my lines.

I keep well documented records/pedigrees on all of my rats.
I also ask those I have sold to, to keep me updated on the health of the rats they got from me.


I have never seen tumors in any of my bred rats so far (as of July 2017). I do have several lines that are new to me. They all come from established well known great breeders who I trust to breed healthy animals.

I have had two adopters report tumors, it was from the same line which was retired for other reasons before the tumors were reported to me..

The first, involved a now retired Russian Blue Line, they contacted me saying their rat had developed a tumor. Personally I believe it was instead likely an abscess and not a tumor as he was a very young male. Abscesses often get confused for tumors. The person sadly refused to see a vet or return him to me so I can not say for sure. None in that line have had any health issues.

The second person was also from that Russian Blue line, both of their female rats developed tumors and were euthanized at the same time. None of the rats I kept from this line developed tumors.



I have only actually ever dealt with one tumor and it was with one of my very first pet rats, far before I ever bred. I first got into rats with a pair of girls from a local pet store forever ago. My girl Sookie was almost 2 years old when she developed a tumor. It grew fairly fast and she passed away. It was heartbreaking for me and almost made me give up on rats completely, but I just loved them too much. It probably played a heavy role in me deciding to breed all these years later!




For more info:

The genetic components of susceptibility to breast cancer in the rat:

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