Sessile serrated adenomas (SSA) are potentially responsible for the apparition of
interval colorectal cancer (CRC) [1]. Their malignant transformation does not follow
the classical molecular pattern [2].
SSA are more difficult to detect in endoscopy. The endoscopic diagnosis is based on
white light imaging (WLI) and narrow band imaging (NBI) with magnification, using
the WASP criteria [3].
We report here 2 atypical nongranular LSTs that had both sessile serrated criteria
(WASP) but also a classical adenoma/adenocarcinoma component. ESD was performed using
the clip-traction strategy [4].
First patient had a 3 cm non-granular lateral spreading tumour (LST) in the left colon,
Paris IIB, with Kudo Vi pit pattern but also crypts with dark spots (Figure 1,2).
En bloc ESD was performed. We closed the large mucosal defect with clips and a rubber
band [5]. Histology revealed complete resection of a degenerated SSA with in-situ
carcinoma.
The second patient had a cm non-granular LST was found on the sigmoid, Paris 0-IIa
+ 0-IIc, Kudo Vn with nearly avascular capillaries (Sano IIIB) (Figure 3). ESD was
performed because of comorbidities and high surgical risk. Histology revealed complete
resection of a SSA with a focal moderately differentiated adenocarcinoma that was
deeply invading (2200 µm) the submucosa, tumoral budding but no vascular or lymphatic
invasion. Complementary surgical intervention was recommended.
Both this lesions had 2 distinct components: a classical adenomatous and also a sessile
serrated one with dark spots inside crypts, a clouded surface and irregular shape.
There were no complications after ESD.
Malignant transformation has rarely been described within a SSA but appears as a conventional
adenomatous malignancy. In those transformed lesions, two components are clearly identified.
Endoscopic evaluation using NBI with dual focus magnification is very important, in
order to decide for the best resection strategy based on the worst component after
histology prediction.
