Oh Lisa, so sorry to hear about Halo! I know exactly what you are going through, me little 6 year old Yorkie had cancer, the tumor they removed from between his shoulder blades also contained the microchip....we had to send him on to the big dog park in the sky on May 27, just covered with tumors.
We tried treatments and chemo but they made him so sick we stopped .....trying to help him live longer but so sick would have been for us, not him. We miss our sweet boy so much!
I belong to a small group of pet owners whose pet also experienced cancer after microchipping....and the chip makers ought to be ashamed of themselves, they still maintain that these chips are completely safe!
We will have a web site up and running in the next week or so where pet owners can report/register adverse reactions in their pets from microchips...please check it out at www.chipmenot.com
Again, so sorry about Halo....we need to be strong and loud in our objections to chips!