What is this on my dogs leg

Are there any vets? Or vet techs in here? This is on my sister in laws dog. She's taking him in tomorrow but wanted me to ask on here... Anyone know what it might be?

Hello!  There are multiple possibilities for lumps in general, including cysts or cancers (benign or malignant) or sometimes foreign bodies emerging from beneath.  It is possible that a vet may not be able to diagnose a lump without removing a sample and sending it off for histology - and not always then.  However, a diagnosis is often useful because it can help a vet to find out how to expect a lump to behave; whether chemotherapy may be needed, or further tissue removal, or antibiotics.  Various of our vets have written about lumps in the blog; if you search for 'lump,' you will find several good articles.  Best of luck.

I would be very interested to hear from your sister-in-law how things eventually go with this one.