To the Editor.—Sessile serrated lesion (SSL) has gained considerable interest recently, and particularly since its discovery as an important neoplastic precursor in the colon. This is not only reflected in the large number of publications on this entity in the past 10 years, but also in the multitude of terms used to describe it. As pathologists, our armamentarium of diagnostic terms represents the language of our profession, the power of our voice, so of course it is important to be accurate scientifically; as best as possible, we should name disorders based on science rather than art. I will try to provide some clarification and rationale for the recent change of the term “Sessile Serrated Adenoma/Polyp” (SSA/P) to “Sessile Serrated Lesion (SSL),” as put forth in the most recent 5th edition of the World Health Organization (WHO) classification of digestive system tumors, published in 2019.1  As an expert member of the WHO scientific committee who participated in the development of this book, I was asked to write a commentary on the results of the international survey on attitudes toward the diagnostic term SSL.2  However, before I do that, I will attempt to provide some historic perspective that led to the proposed change in terminology. In 2010, when the gastrointestinal (GI) scientific panel (which consisted of pathologists from many countries around the world) met in Lyon, France, to lay the groundwork for the 4th edition WHO book on digestive tumors,3  a spirited debate occurred between members of the GI panel regarding the term that we would ultimately recommend for flat serrated colonic lesions that were known to have malignant potential. At that meeting, proponents of the term “adenoma” cited its neoplastic potential, similar to conventional adenomas, as the main reason for use of that name. However, others at the meeting believed that use of that term would falsely imply to our gastroenterology colleagues that all of these lesions are morphologically dysplastic (because all colonic adenomas are, in fact, dysplastic). Furthermore, some pathologists at the meeting also expressed concern over use of the term “adenoma with cytologic dysplasia,” when the latter morphologic changes were identified in the lesion, because this would offer confusion (eg, if all colonic “adenomas” are, by definition, dysplastic then the term “adenoma with dysplasia” might be construed by physicians as both confusing and redundant). As a result, the term “polyp” was proposed by some members of the committee to convey a more “neutral” biological perspective, with the hope that this term would be less confusing to our GI colleagues. Unfortunately, the term “polyp” was also not necessarily scientifically accurate because most SSLs are not, in fact, polypoid, but instead are typically flat, occasionally imperceptible, mucosal irregularities with indistinct borders. Regardless, the expert panel members voted on their preferred term and, as expected, the results were mixed. Thus, as a compromise, the term “SSA/P” was born. In the ensuing 10 years, anecdotally, the term had not gained widespread acceptance among either pathologists or gastroenterologists mostly for the reasons cited above, and also because we now created a diagnostic term that readily morphed into at least 3 other variations (SSP/A, SSA, and SSP, among others). As a result, at the most recent 5th edition WHO planning committee meeting,1  the pathology participants were challenged with the task of correcting the mistakes of the past and, thus, were resigned to propose a new term for this “lesion” that would serve a number of the following goals: (1) consolidate the plethora of terms used in the past into 1 term that would be widely accepted both clinically and in research; and (2) create a term that, as best as possible, would be biologically and pathologically accurate. The term SSL seemed to serve both of these purposes and, not surprisingly, was unanimously accepted by members of the committee from all corners of the world, including the US. The committee was particularly satisfied with the more neutral term “lesion” (instead of adenoma or polyp), which is commonly defined as “an area of abnormal tissue change that can be either benign or malignant”. This term served to remedy the “adenoma” and “polyp” dilemma (as discussed above), and also is used quite commonly in pathology when one wants to remain neutral and unbiased about a disorder that does not quite fit nicely into a single textbook description.

Given the circumstances of how we got here, and knowing that pathologists are well known for bringing their own knowledge and beliefs and experiences to the table when offering scientific opinions, the results of the international survey are not at all surprising. Here are a few observations on the data that I find of particular interest: (1) Pathologists from the US, not uncommonly, have different views and, in some cases, are less “progressive” (personal opinion) on many issues in GI pathology compared with our European and Asian colleagues. This is clearly reflected in the survey, where a much higher proportion of non-North American respondents voted in favor of using the term SSL going forward. Perhaps the fact that the WHO is based in Europe and commonly viewed as a non-North American medical society played a role in that result? (2) Only 25% of the pathologists involved in the survey ever adopted the term SSA/P that was recommended in the 2010 WHO classification of digestive tumors, but 39% expressed the desire to use the new term SSL.2  This could be construed as progress. (3) When asked for the specific reason why one would not use the new term SSL, 85% of participants responded that it “might confuse /frustrate my gastroenterology colleagues.”2  However, as I mentioned above, my own anecdotal experience and perceptions created by interacting with hundreds of physicians in medical-based GI societies during the past 10 years is that they are already confused and frustrated by the inconsistency and variety of terms used to describe this lesion and the apparent lack of scientific basis for them.

Despite ongoing, and I would argue, healthy differences in each of our own individual philosophies, criteria, experiences, and beliefs, especially between individuals of different cultures, acceptance of new terminologies will always be with us until at least the time that science provides us with proven concepts and truths. Until then, the WHO pathology panel approach to using the term “lesion” rather than adenoma or polyp is sound. Ultimately, the most important thing we should do as pathologists is to make sure that, despite our differences of opinion and regardless of the terms used to describe any particular disorder, our GI colleagues understand the true clinical relevance and biology of the lesions we report to them. Ultimately, being on the same page with our GI physicians is best for patient care.

Colorectal serrated lesions and polyps
WHO Classification of Tumours Editorial Board, ed. WHO Classification of Tumors: Digestive System Tumours. 5th ed
Lyon, France
International Agency for Research on Cancer;
Attitudes regarding the World Health Organization-recommended term “sessile serrated lesion.” Results from an international survey
Arch Pathol Lab Med.
Serrated polyps of the colon and rectum and serrated polyposis
WHO classification of Tumors of the Digestive System 4th ed
Lyon France
International Agency for research on cancer;

The author has no relevant financial interest in the products or companies described in this article.