. 2024 May 9;111(5):znae070. doi: 10.1093/bjs/znae070

Table 26.

Statements pertaining to other rare adenomatous polyposis syndromes (OAPS)—extended version

Statements
OAPS.1 In which patients should germline screening for inherited types of adenomatous polyposis syndromes be performed? A. Germline multigene panel testing should be considered in patients with >20 cumulative colorectal adenomas. 1B. The threshold may be lowered to 10 cumulative adenomas if: Diagnosed under the age of 60, or Family history of polyposis or CRC, or Extracolonic manifestations consistent with known polyposis syndromes. C. Germline multigene panel testing (for CRC and polyposis syndromes) should be undertaken in patients with GI cancers presenting under the age of 50 years. D. Somatic testing for APC mosaic mutations should be considered in unexplained polyposis patients fulfilling criteria from statements A and B.
OAPS.2 What is the best strategy for predictive testing in first-degree relatives? A. In the case of autosomal recessive hereditary polyposis syndromes, testing should always be offered to siblings. Children should be tested when: the frequency of carriers of pathogenic variants in the corresponding gene is higher than 1 in 100 in the general population; parents are consanguineous; monoallelic alterations in the corresponding gene also cause increased risk of cancer (for example MMR gene mutations in relative of CMMRD patients). In this last case, testing should be offered to all first-degree relatives followed by cascade testing. B. In autosomal dominant polyposis syndromes, testing should be offered to all first-degree relatives followed by cascade testing.

Statements

OAPS.1 In which patients should germline screening for inherited types of adenomatous polyposis syndromes be performed?
A. Germline multigene panel testing should be considered in patients with >20 cumulative colorectal adenomas.
1B. The threshold may be lowered to 10 cumulative adenomas if:

Diagnosed under the age of 60, or
Family history of polyposis or CRC, or
Extracolonic manifestations consistent with known polyposis syndromes.

C. Germline multigene panel testing (for CRC and polyposis syndromes) should be undertaken in patients with GI cancers presenting under the age of 50 years.
D. Somatic testing for APC mosaic mutations should be considered in unexplained polyposis patients fulfilling criteria from statements A and B.

OAPS.2 What is the best strategy for predictive testing in first-degree relatives?
A. In the case of autosomal recessive hereditary polyposis syndromes, testing should always be offered to siblings. Children should be tested when:

the frequency of carriers of pathogenic variants in the corresponding gene is higher than 1 in 100 in the general population;
parents are consanguineous;
monoallelic alterations in the corresponding gene also cause increased risk of cancer (for example MMR gene mutations in relative of CMMRD patients). In this last case, testing should be offered to all first-degree relatives followed by cascade testing.

B. In autosomal dominant polyposis syndromes, testing should be offered to all first-degree relatives followed by cascade testing.

CMMRD, congenital mismatch repair deficiency; CRC, colorectal cancer; GI, gastrointestinal; MMR, mismatch repair.