It would be very common, especially in HPV+ oropharyngeal cancers, for the primary to be non visible or occult on physical visual exam with a scope. These things can be buried deep in the tonsillar tissue, the tonsillar crypt, or in the lymph tissue on the base of the tongue for quite some time before producing a surface lesion.

7-8 years ago doctors were calling these an "unknown primary" when you had a cervical node (which is never the primary) positive for SCC and an occult oral environment. We subsequently learned how these HPV+ cancers seldom present with surface lesions, and because they metastasis to the neck through the normal lymph drainage passageways very rapidly, the primary can be even too small to see in a scan. Everyone was shocked when OCF sponsored at study at Johns Hopkins and we determined that the primaries could be a small as 2-3 mm in size, and be spinning off mets to the cervical nodes. That was unheard of at the time, as usually a primary has to be much larger before it metastasizes. But the unique location of these cancers directly within the lymph chain allowed it.

Remember that all new cells, and cancer cells included, begin in the basal layers of the epithelium which is relatively deep in the architectural structure of tissue, and migrate towards the upper epithelium that you can see.

Note that a subsurface 2-3mm primary can be easily missed even by a CT scan that looks at slices of your body about 3-5 mm apart. And unfortunately these "unknown primary" patients got radiated in much larger fields unnecessarily since a specific target was not found. The most likely areas were nuked. Wild ideas were postulated at the time like, a person's immune system had finally kicked in and taken care of the primary leaving the node in the neck untouched. Really? A systemic defensive mechanism goes after one little thing and the other cancer locations it leaves alone? Nonsense. But we had posters here that were told that.

For a much informative but not hard science read, I found "The Emperor of all Maladies" a great book which in a very readable and entertaining way chronicles cancer treatment in the US from the 1940's to present day. It is scary to read about the things we were doing into the 1950's and 60's to people with no idea if it would work or not, no controls or even the idea of a proper clinical trial, including massive radiation dosages to the chest (and heart) of women that had breast cancer. Of course in the 1940's no one survived treatment. But it is all there to read and the formation of the American Cancer Society is well covered too, which had a few interesting twists in it. We have come a long way, but it just reinforces in my mind how far we have yet to go.