Inbreeding IMHO should be the last resort to save a breed from extinction, but not to enhance an existing breed with a large gene pool. Yes it would bring out purity or traits of a breed, but it's also guaranteed to bring out genetic faults via autosomal recessive genes matching up. Can increasing the genetic burden in a breed be considered good for the breed?

Clumping- I plead guilty as per my first post in this thread. The idea being that no matter how noble the intent, most breeders are going to concern themselves with the top 2-3 faults in a breed. Very few if any especially if they are in it as their business are going to screen for genetic related disease that may show increased incidence but are not considered to be the most important genetic faults. None are likely to worry about cancer oncogenes being present in their stock or progeny.

BTW- out of curiosity I remembered today seeing a mention of an article discussing the incidence of Lymphoma in canine breeds. So I looked it up, and read it. It appears in a British Vet Journal , but I didn't remember to write down the citation for it. In the article they did an epidemiology study of the disease in the UK. They listed 21 breeds where #21 was labeled all other breeds as a catch-all. Of the 20 breeds named: Boxers, Bulldogs, and Mastiffs topped the list. The Border Collie came in 9th.

In looking up the Boxer there are 26 possibly inherited health concerns with it. Lymphoma does not make the list. Bets here are that you won't find a breeder concerned with keeping track of the incidence of cancer in the puppies s/he is producing. Clumped again!