A biopsy may not give the whole story
Surely when you get a final pathology report from a biopsy you have a definitive diagnosis? Well not always. While diagnosing a basal cell carcinoma or squamous cell cancer is usually pretty straightforward, the biopsy is only a sample of a larger tumor. So what is seen on the biopsy may not be identical to what is present in the rest of the tumor. This is not to say that what was diagnosed a basal cell cancer could really be a melanoma or anything like that. However there are many different sub-types of basal cell and squamous cell cancer, and some of them are a lot more aggressive than others. So while the biopsy may show a non- aggressive sub-type a more complete analysis may show areas of more aggressive disease that would require a wider surgical margin to remove. This is another instance where Mohs surgery seems to be beneficial. In a recently published study it was found that during Mohs surgery for basal and squamous cell cancers the Mohs surgeon found evidence of more aggressive disease more than 10% of the time. These cases were more likely to need more Mohs stages. Had an other treatment modality been used it is likely that this aggressive component of the tumor would be missed and some cancer be unwittingly left behind.
Histopathologic upgrading of nonmelanoma skin cancer at the time of Mohs micrographic surgery: A prospective review
Rachel L. Kyllo, MDa, Karl W. Staser, MD, PhDa, Ilana Rosman, MDa,b, M. Laurin Council, MDa,c, Eva A. Hurst, MD
JAAD August 2019 Volume 81, Issue 2, Pages 541–547