how can I tell if my dog has cancer?

Question
I have a Rottwieler and pitbull mix that is almost 4 and she was very malnutrishend as a  puppy and she is overweight. About two weeks ago I woke up and noticed that she was having a hard time walking well since then it has only gotten worse. It looks as though her back left leg is broken; the knee is kind of popped out and this morning I seen that her front left leg is starting to bother her also. Do you think that it is cancer?

Answer
Hello Mandi;
I know this must be a difficult time for you!
I would urge you to take your dog to the Vet.
Although, the dog is fairly young, being that it is a mixed breeding, there is "No Telling" what the cause is, until the Vet does an exam!
I would say that there are some definite disease issues causing her body to breakdown, whether it is cancerous, only a test can verify for sure. It could be a simple fix like a weight reduction to allow her joints and ligaments to ease from the stress of the extra poundage, but, probably there is something underlying and may be a bigger problem for sure. If it is Connective Tissue Stress allowing the structure to give way, there are "Glucosomine" products available everywhere to help these type of issues...but, again, a Vet, will confirm what is the "True" underlying problem(s), and give you the correct prognosis.

As difficult as this is for you to hear, truly, it may be time to put her to sleep, if she is continuously suffering, it is not fair for her, or for you either.

Please do take the time to let me know what you have decided in the future, I would love to hear back from you.

Best wishes during this time for you and your friend!
Regards,
Melissa

P.S. let me know if there is anything else I can assist you further with.
And please feel free to give me a rating on the site, which would most suit my answer.