It looks like, same as for your link, SEER classifies tissues using the ICD-O-3 scheme: https://seer.cancer.gov/icd-o-3/ https://seer.cancer.gov/icd-o-3/ So if

It looks like, same as for your link, SEER classifies tissues using the ICD-O-3 scheme: https://seer.cancer.gov/icd-o-3/ https://seer.cancer.gov/icd-o-3/ So if there is a cancer called "Papillary squamous cell carcinoma, non-invasive", I would want a count of "papillary squamous cells".