Clinicopathological study of squamoid morules in nineteen conventional colorectal adenomas

Squamoid morules are an intriguing finding rarely seen in colorectal adenomas, mimicking foci of microinvasion or neuroendocrine differentiation. We identified nineteen colorectal adenomas with squamoid morules and collected clinicopathological data. A representative block was chosen for immunohistochemistry. The expression of p40, p63, CK5/6, beta-catenin, synaptophysin, chromogranin, and Ki-67 in squamoid morules were examined immunohistochemically. The nineteen patients comprised fifteen males (79%) and four females (21%) ranging in age from 45 to 85 years (average: 59.4 years old). Fourteen adenomas were tubulovillous adenomas (average: 3.4 cm, ranging 1.0 to 6.0 cm) and five were tubular adenomas (average: 2.6 cm, ranging 1.6 to 3.0 cm). All foci of squamoid morules showed beta-catenin nuclear positivity and CK5/6 expression. Squamoid morules were focally positive for p63 in four adenomas and focally positive for p40 in two adenomas. In two adenomas squamoid morules are focally positive for synaptophysin, and in one adenoma chromogranin was focally positive. In all nineteen adenomas squamoid morules were negative for Ki-67. Squamoid morules are characterized by strong male predominance, large adenoma size, beta-catenin nuclear positivity, CK5/6 expression, and no Ki-67 expression. Beta-catenin nuclear expression is helpful in distinguishing squamoid morules from foci of microinvasion and neuroendocrine differentiation.