The Math of Margins: A Fresh Look at Bread Loaf Sections, Unchallenged Assumptions, and Citogenesis

Although there are many possible ways to treat skin cancer, most skin cancers are effectively treated by complete excision followed by standard histologic evaluation to ensure clear margins. The bread loaf technique describes a common method of processing specimens in which multiple slices of tissue are taken perpendicular to the major axis of an excision and submitted for microscopic analysis. Although sections may only be approximately four microns thick (0.000004 meters), this method is associated with high cure rates for basal cell and squamous cell carcinoma. Some authors have stated that this technique assesses less than 1% of the margins. We critically reviewed this assumption. While we confirm that the bread loaf technique often directly visualizes 1% or less of the peripheral and deep margins when considering only the width of sections compared to the entire length of an excisional specimen of the excision, much useful additional information is gained as soon as clear sections are identified towards the tips of a typical excisional specimen. For tumors that tend to grow in a nodular or spherical arrangement such as nodular basal cell carcinoma or squamous cell carcinoma of keratoacanthomatous type, we show that a variable but significant portion of the margin may be considered sampled by proxy when slice faces are clear. We highlight the importance of understanding the principles involved in tissue sectioning in order to allow clinicians to make informed decisions on behalf of patients.