Discussion

The architectural feature of serration was attributed to adenomatous polyps by Longacre and Fenoglio-Preiser7 in 1990, who introduced the term ‘serrated adenoma’. However, this terminology was applied for the most part to lesions that we recognise today as ‘traditional serrated adenoma’.6 SSA/P were distinguished from hyperplastic polyps in 1996 when a detailed histopathological examination of the polyps present in ‘hyperplastic polyposis’ revealed subtle but important differences from sporadic hyperplastic polyps.8 The hallmark of uncomplicated SSA/P is ‘architectural dysplasia’ and evidence of ‘dysmaturation’ believed to be secondary to displacement of proliferation zone from the muscularis mucosae.8 This results in an abnormal shape of the crypts as well as the proliferation zone and maturation sequence being altered and detected in unexpected areas away from muscularis mucosae.8 ,9 It is now believed that these changes are intrinsic to SSA/P. Furthermore, conventional, adenomatous-type dysplasia (low-grade and high-grade) and colorectal cancer (CRC) can develop within SSA/P via the serrated pathway.6 ,7 SSA/P are believed to be more common in the right colon, often attain a size of >10 mm and contain genetic alterations distinct to those of ‘classical’ adenomas. It is postulated that progression to CRC along this serrated pathway may occur at a faster rate than via the chromosomal instability adenoma-carcinoma sequence. In particular, BRAF mutations and DNA methylation across the genome, leading to the CpG island methylator phenotype, are commonly present.10 The latter event results in microsatellite instability and loss of DNA mismatch repair protein (especially hMLH-1 and PMS-2) expression within areas of conventional dysplasia and CRC, when they arise in association with SSA/P.10

Recognition of the neoplastic potential of SSA/P has led to recommendation that these polyps should be managed differently to hyperplastic polyps.2 There is growing acceptance of the need for complete local excision of SSA/P and for endoscopic follow-up that is broadly similar to that recommended for classical adenomas of similar size.2 This contrasts markedly with patients in whom hyperplastic polyps are identified and for the majority of whom no further surveillance is needed.

The implications for patient management following the diagnosis of a lesion as a SSA/P rather than a hyperplastic polyp mean that accurate recognition of SSA/P by histopathologists is essential.

Despite several publications in the last 10 years, SSA/P remains an enigmatic and underdiagnosed entity.11–14 Its absence as a diagnostic entity in some polyp surveillance programmes (such as the bowel cancer screening programme in the UK, which is in the process of being revised), has compounded the lack of awareness. Given its importance, it is incumbent on the pathologist to identify these precancerous lesions. The intent of this survey was to ascertain the degree of consensus among a diverse range of pathologists with regards to SSA/P.

The overwhelming majority of participating pathologists were aware of the implications and importance of SSA/P. However, over one-third of pathologists did not know, or believed that their clinical colleagues were aware, of the implications of SSA/P. This may tie in with the absence of surveillance programmes in several institutions and was pointed out in 2009 by Pettus and colleagues.15 In a survey of 52 university and community hospital-based gastroenterologists, 40% were unaware that SSA and SSP were the same lesion; 50% claimed that they received a diagnosis of SSA/P with an accompanying note in the pathology report, and 73% thought SSA/P showed conventional adenomatous change and were variants of tubular/tubulovillous adenomas.15 Almost all participants (98%), however, were aware that SSA/P were indeed precursor lesions to CRC.15 This discordance of awareness, and/or knowledge about SSA/P between pathologists and clinicians, is of concern, and should be a major focus of education sessions and even routine multidisciplinary team meetings. Despite knowing that clinicians might be unaware of SSA/P, over one-third of participants still did not enter a comment flagging the importance of SSA/P in the pathology report. We believe that the pathologist should take the lead in this role as they make the diagnosis, and appear to be well informed about the entity.

SSA/P is characterised by the presence of several morphological features that are not seen in other serrated polyps (hyperplastic polyps or traditional serrated adenomas). However, there is not yet complete agreement as to which of these are the most important or useful and crucially, how widespread they need to be to make a diagnosis of SSA/P. All participating pathologists did agree that architectural abnormalities of the gland/crypt were diagnostic of SSA/P. The survey has shown that the major differences of opinion and difficulties lie in defining the minimum diagnostic criteria and in terminology. It is apparent that the ACG guideline of a single crypt showing unequivocally typical SSA/P features, is not universally adhered to, and the majority of participants (70%) required diagnostic features to be present in more than one crypt. Additionally, the single histologic feature that all pathologists required was the presence of dilated crypts displaying the characteristic architecture. When these changes are well developed, especially in larger SSA/P, then the diagnosis can be made with relative ease. The difficulty lies in small and/or poorly oriented biopsies. The group of participants in this survey almost unanimously used levels to facilitate the diagnosis. Furthermore, our future understanding of the biological importance of these lesions will need to include a clearer elucidation of the risk of disease progression in relation to the minimum diagnostic criteria required, and to other features, such as the lesion size and anatomical location.

The vast majority of participants (81%) were diagnosed with SSA/P in the right and left colons. Although there is a distinct predilection for the right colon, left-sided SSA/P do exist, and should be diagnosed once histological mimics (especially mucosal prolapse with hyperplastic tubules) have been excluded.3 There is no doubt that bona fide examples of SSA/P do exist in the left colon, and the same histological criteria should be applied in this location as when assessing right-sided lesions.14

A brief discussion regarding terminology raised some divisions around the use of the term, ‘SSL’. Although not an integral part of the survey, the inevitable trans-Atlantic divide on nomenclature did surface. ‘SSL’ is a Eurocentric term and endorsed mainly by UK/European pathologists.16 Some North American participants appeared sanguine about its use, while others were more opposed to the term. There is a contention that using the term ‘adenoma’, by definition, traditionally implies the presence of ‘conventional’ cytological dysplasia, and that ‘lesion’, on the other hand, is perhaps too vague a descriptor. Although the vast majority of SSA/P do not show ‘conventional’ cytological dysplasia, it is ‘architectural dysplasia’ that defines SSA/P. In most non-epithelial tissues, the term ‘dysplasia’ is not limited to nuclear atypia, as it is in preinvasive neoplastic epithelial lesions, but it is used in its alternative and wider meaning/definition, that is, ‘abnormal development or growth of tissues, organs, or cells’. SSA/P is defined by evidence of the abnormal growth of cells in crypts resulting in their disordered development.9 The current terminology that is endorsed by WHO is ‘sessile serrated adenoma/polyp’, but there is a contention, mainly from the UK, that ‘sessile serrated lesion’ be adopted. Suffice it to say, that recognising this characteristic pathology and communicating its importance, no matter what terminology one uses, is the emphasis of this study.

Awareness among clinicians and pathologists needs to increase, and standardised handling and reporting guidelines are needed to ensure greater uniformity and consistency with regards to SSA/P.