What does it mean when they say the specimen is submitted entirely in one cassette, a1?

This is normal: terminology for processing of surgical pathologic specimens. A specimen was obtained from site "A" ...all of it was encased in a little plastic box/cassette, perhaps 2-3" long by 1-2" wide. Only one specimen was obtained and labeled A1. This is simply a description of where they placed the biopsy material. It indicates nothing about the diagnosis or significance of the specimen. Hope this helps.