The abstract says they studied 24 cats with spontaneous hypertension, and tried various drug regimens to lower blood pressure. More recently at this year's American College of Veterinary Internal Medicine, a paper was presented by P.S.Snyder et al on Feline Systemic Hypertension. However I was not at the meeting and do not have the proceedings. Basically there is very little out on hypertension in cats, and it is quite recent. In dogs, the typing process is not so well advanced.
Lymphoma is one of the cancers in dogs that responds reasonably well to chemotherapy.
I do not know of any work that has demonstrated a particular cause of lymphoma in our pets. I don't have data on the carcinogenicity of common flea treatments, but were one to look, I suspect you'd find that countless research animals have had plenty of exposure to these substances to look for this side effect. As far as breed predilections go, it seems that Boxers, Basset hounds, Saint Bernards and Scottish terriers have been found to be at increased risk. So I cannot provide diagnoses, or really tell you to ignore or treat a given problem. I hope the information provided guides you in making good health care decisions for your pets.