CTNNB1 Genotyping and APC Screening in Pediatric Desmoid Tumors: A Proposed Algorithm

Identification of Familial Adenomatous Polyposis carriers among children with desmoid tumours

Lynch syndrome is caused by variants in DNA mismatch repair (MMR) genes and associated with an increased risk of colorectal cancer (CRC). In patients with Lynch syndrome, CRCs can develop via different pathways. We studied associations between Lynch syndrome-associated variants in MMR genes and risks of adenoma and CRC and somatic mutations in APC and CTNNB1 in tumors in an international cohort of patients. We combined clinical and molecular data from 3 studies. We obtained clinical data from 2747 patients with Lynch syndrome associated with variants in MLH1, MSH2, or MSH6 from Germany, the Netherlands, and Finland who received at least 2 surveillance colonoscopies and were followed for a median time of 7.8 years for development of adenomas or CRC. We performed DNA sequence analyses of 48 colorectal tumors (from 16 patients with mutations in MLH1, 29 patients with mutations in MSH2, and 3 with mutations in MSH6) for somatic mutations in APC and CTNNB1. Risk of advanced adenoma in 10 years was 17.8% in patients with pathogenic variants in MSH2 vs 7.7% in MLH1 (P < .001). Higher proportions of patients with pathogenic variants in MLH1 or MSH2 developed CRC in 10years (11.3% and 11.4%) than patients with pathogenic variants in MSH6 (4.7%) (P= .001 and P= .003 for MLH1 and MSH2 vs MSH6, respectively). Somatic mutations in APC were found in 75% of tumors from patients with pathogenic variants in MSH2 vs 11% in MLH1 (P= .015). Somatic mutations in CTNNB1 were found in 50% of tumors from patients with pathogenic variants in MLH1 vs 7% in MSH2 (P= .002). Noneof the 3 tumors with pathogenic variants in MSH6 had a mutation in CTNNB1, but all had mutations in APC. In an analysis of clinical and DNA sequence data from patients with Lynch syndrome from 3 countries, we associated pathogenic variants in MMR genes with risk of adenoma and CRC, and somatic mutations in APC and CTNNB1 in colorectal tumors. If these findings are confirmed, surveillance guidelines might be adjusted based on MMR gene variants.

134 Background: Nirogacestat (niro) is an oral, targeted gamma secretase inhibitor FDA-approved for adults with progressing desmoid tumors (DT) who require systemic treatment. In the phase 3 DeFi trial (NCT03785964), niro demonstrated significant improvement vs placebo (pbo) in progression-free survival (PFS; HR 0.29 [95% CI: 0.15–0.55], P &lt;.001) and objective response rate (ORR; 41% vs 8%, P &lt;.001). Most DT are sporadic tumors characterized by somatic mutations in the CTNNB1 gene. About 10%–20% of DT are associated with APC mutations, the majority being germline that may cause familial adenomatous polyposis (FAP), an inheritable trait linked to an increased risk of colorectal cancer and may also confer more aggressive DT behavior. Methods: In DeFi, adult patients (pts) were randomized to oral niro (150 mg) or pbo twice daily. In pts with evaluable blood and tumor samples, descriptive post hoc analyses assessed effects of niro in pts with germline and/or somatic APC mutations, including pts with co-occurring somatic mutations of APC and CTNNB1 . Results: Of the 142 pts in DeFi, 29 pts had APC mutations (niro=13, pbo=16; 22 somatic, 21 germline, and 14 somatic and germline), including 3 pts (niro=2, pbo=1) with co-occurring somatic mutations of APC and CTNNB1 . Of these 29 pts, 19 (66%) were female, 16 (55%) were aged ≤30 y, 22 (76%) had a family history of FAP, and 22 (76%) were refractory to prior therapy (median of 3 prior lines of therapy). PFS was improved with niro vs pbo (HR 0.21 [95% CI: 0.05–1.00], P =.016). Confirmed ORR was 38% (5/13) for niro vs 13% (2/16) for pbo; median time to response with niro was 8.31 months. All 3 pts with co-occurring somatic mutations of APC and CTNNB1 were female, aged 18–56 y, had DT in the upper extremity or abdominal wall, and had no family history of FAP. The 2 pts on niro had received prior systemic therapy and/or surgery and the 1 pt on pbo had no prior therapy. Of the 2 pts on niro, both achieved a partial response (median time to response: 9.9 months). The 1 pt randomized to pbo experienced disease progression in 2.6 months. In pts with APC mutations, diarrhea was the most frequently reported adverse event. In niro-treated pts, increased rates of skin events (maculopapular rash, 62%; dermatitis acneiform, 38%) and stomatitis (46%) were reported in pts with APC mutations compared with those in the overall DeFi population (32%, 22%, and 29%, respectively). Conclusions: Improvement in PFS and ORR was observed with niro vs pbo in pts with DT harboring APC mutations. Efficacy and safety of niro in pts with APC mutations were generally consistent with findings for the overall DeFi population. Although analyses were limited due to small sample size, these results suggest that niro can provide clinically meaningful benefit to pts with progressing DT and APC mutations, including those with co-occurring somatic mutations of APC and CTNNB1 . Clinical trial information: NCT03785964 .

ColoSeq Provides Comprehensive Lynch and Polyposis Syndrome Mutational Analysis Using Massively Parallel Sequencing

Desmoid tumours (also called deep or aggressive fibromatoses) are potentially life-threatening fibromatous lesions. Hereditary desmoid tumours arise in individuals affected by either familial adenomatous polyposis (FAP) or hereditary desmoid disease (HDD) carrying germline mutations in APC. Most sporadic desmoids carry somatic mutations in CTNNB1. Previous studies identified losses on 5q and 6q, and gains on 8q and 20q as recurrent genetic changes in desmoids. However, virtually all genetic changes were derived from sporadic tumours. To investigate the somatic alterations in FAP-associated desmoids and to compare them with changes occurring in sporadic tumours, we analysed 17 FAP-associated and 38 sporadic desmoids by array comparative genomic hybridisation and multiple ligation-dependent probe amplification. Overall, the desmoids displayed only a limited number of genetic changes, occurring in 44% of cases. Recurrent gains at 8q (7%) and 20q (5%) were almost exclusively found in sporadic tumours. Recurrent losses were observed for a 700 kb region at 5q22.2, comprising the APC gene (11%), a 2 Mb region at 6p21.2-p21.1 (15%), and a relatively large region at 6q15-q23.3 (20%). The FAP-associated desmoids displayed a significantly higher frequency of copy number abnormalities (59%) than the sporadic tumours (37%). As predicted by the APC germline mutations among these patients, a high percentage (29%) of FAP-associated desmoids showed loss of the APC region at 5q22.2, which was infrequently (3%) seen among sporadic tumours. Our data suggest that loss of region 6q15-q16.2 is an important event in FAP-associated as well as sporadic desmoids, most likely of relevance for desmoid tumour progression.

Desmoid Tumors in a Dutch Cohort of Patients With Familial Adenomatous Polyposis

Inherited Polyposis Syndromes: Molecular Mechanisms, Clinicopathology, and Genetic Testing

Disclosure: D. Caesario: None. M.S. Richardson: None. D. Carneiro-Pla: None. J.K. Fernandes: None. Introduction: Cribriform morular thyroid carcinoma (CMTC) is a rare thyroid cancer that is classically associated with familial adenomatous polyposis (FAP), but can also occur sporadically. We report a case of CMTC in a young female with history of whole-body radiation therapy (WBRT). Case Report: A 19-year-old female with past medical history of Wilms’ tumor (WT) with lung metastasis status post left nephrectomy and WBRT at the age of 6 was seen for newly diagnosed thyroid nodules. Physical exam was remarkable for thyromegaly. Thyroid function tests were normal. Thyroid ultrasound revealed 2 dominant TI-RADS 4 nodules measuring 1.9 x 1.7 x 2.1 cm on the left lobe and 0.9 x 0.8 x 0.8 cm on the right lobe. No suspicious lymphadenopathy. Fine needle aspiration biopsy on both nodules showed findings consistent with papillary thyroid carcinoma (PTC). No family history of thyroid disorders, malignancies, or FAP. She underwent total thyroidectomy with central neck node sampling. Thyroid gland surgical pathology result revealed CMTC positive for thyroid transcription factor-1 (TTF-1), β-catenin, and cytokeratins 5 and 6. It was negative for calcitonin. There was no evidence of invasion, extension, or lymph node metastasis. Genetic tests are currently pending. Discussion: CMTC was previously considered a variant of PTC, accounting for 0.2 to 6% of PTC cases. However, recent observations have challenged this view, and latest WHO update reclassified it as a distinct form of thyroid cancer. It is associated with an indolent clinical course and good prognosis. It almost exclusively affects young women. Both familial and sporadic cases are associated with mutations in the adenomatous polyposis coli (APC) gene. The APC protein is a negative regulator that controls β-catenin concentrations, which is involved in cell adhesion. Mutations in the APC gene may result in FAP and colorectal cancers. In cases associated with FAP, the tumors are usually multifocal and/or bilateral, while sporadic cases usually appear as single nodule. Tumor cells are always positive for TTF-1 and negative for calcitonin. They can also be positive for multiple cytokeratins, but strong nuclear and cytoplasmic staining for β-catenin is the hallmark of this tumor type. The case above occurred in a young female with no significant family history, but who underwent WBRT for WT as a child. Radiation is a known predisposing factor for thyroid cancer, and limited studies on early exposure to radiation revealed higher incidence of sporadic CMTC. However, even among FAP associated cases, CMTC diagnosis preceded that of FAP in up to 40% of the cases. Additionally, up to 20% of WT cases have mutations of the WT1 gene, and among these, at least half also carry acquired somatic mutations in CTNNB1, the gene encoding β-catenin. So far, there has been no reported case of CMTC in the background of WT. It will be interesting to see if she has these underlying mutations. Presentation: Thursday, June 15, 2023

Adenomatous polyposis coli (APC) is mutated in most colorectal cancers. APC downregulates nuclear beta-catenin, which is thought to be critical for its tumour suppressor function. However, APC may have additional and separate functions at the cell periphery. Here, we examine polarized MDCK and WIF-B hepatoma cells and find that APC is associated with their lateral plasma membranes. This depends on the actin cytoskeleton but not on microtubules, and drug wash-out experiments suggest that APC is delivered continuously to the plasma membrane by a dynamic actin-dependent process. In polarized MDCK cells, APC also clusters at microtubule tips in their basal-most regions. Microtubule depolymerization causes APC to relocalize from these tips to the plasma membrane, indicating two distinct peripheral APC pools that are in equilibrium with each other in these cells. Truncations of APC such as those found in APC mutant cancer cells can neither associate with the plasma membrane nor with microtubule tips. The ability of APC to reach the cell periphery may thus contribute to its tumour suppressor function in the intestinal epithelium.

Hepatoblastoma (HB) is the most frequent liver tumor in childhood, occurring in the first few years of life. Surgery combined with chemotherapy has resulted in dramatic improvements in prognosis. However, even today, about one quarter of affected children do not survive the disease. Compared to the general population, the risk of HB is 750-7,500 times higher in children predisposed to familial adenomatous polyposis (FAP), an autosomal-dominant cancer predispostion syndrome caused by germline mutations in the tumor suppressor gene APC. Only limited data exist about the frequency of APC germline mutations in cases of apparently sporadic HB without a family history of FAP. In our sample of 1,166 German FAP families, all known cases of HB were registered. In addition, 50 patients with apparently sporadic HB were examined for APC germline mutations. In the FAP families, seven unrelated cases of HB are documented; three had been detected at an advanced stage. In patients with apparently sporadic HB, germline mutations in the APC gene were identified in 10%. These data raise the issue of the appropriate screening for HB in children of FAP patients. To date, the efficiency of surveillance for HB is unclear. In Beckwith-Wiedemann syndrome (BWS), recent studies suggest an earlier detection of both Wilms tumor and HB by frequent screening. We discuss the rationale and implications of a screening program; besides the examination procedure itself, screening for HB in children of FAP patients would have important consequences for the policy of predictive testing in FAP. In a substantial fraction of sporadic HB, the disease is obviously the first manifestation of a de novo FAP. These patients should be identified by routine APC mutation screening and undergo colorectal surveillance thereafter.

Inactivation of the adenomatous polyposis coli (APC) gene has been shown to initiate the majority of colorectal cancer (CRC), including a familial form called familial adenomatous polyposis (FAP). One consequence of the APC mutation is the activation of the beta-catenin (CTNNB1)/T-cell transcription factor (Tcf) pathway. A recent study has shown that about half of the sporadic CRC lacking APC mutation has CTNNB1 mutation, suggesting that CTNNB1 mutation can substitute for APC mutation in the initiation of colorectal tumorigenesis. However, the frequency of CTNNB1 germline mutation in FAP has not been reported. In the present study, we investigated the frequencies of APC and CTNNB1 germline mutations in 26 unrelated FAP families. We used the Protein Truncation Test (PTT) to screen the entire coding region of APC and found germline mutations in twenty families. We then screened for CTNNB1 germline mutations in the rest of the families lacking detectable APC mutations. No missense mutations at GSK-3beta phosphorylation sites or interstitial deletion of exon 3 of CTNNB1 was found. Our results indicate that APC germline mutations are frequent but CTNNB1 germline mutations are rare in FAP patients, suggesting that CTNNB1 mutation cannot substitute for APC mutation in the initiation of FAP. Genes Chromosomes Cancer 25:396-398, 1999.

A Porcine Model of Familial Adenomatous Polyposis

Desmoid fibromatosis (DF) is a locally aggressive soft tissue neoplasm with frequent recurrences. DF is characterized by alterations in the Wnt/β-catenin pathway, with the majority showing sporadic mutations in CTNNB1 , whereas others have germline mutations in APC . Immunohistochemical staining for β-catenin is often difficult to interpret and can be negative in up to 30% of cases. Prior studies have shown that some DFs lacking nuclear expression of β-catenin may carry activating CTNNB1 mutations. Droplet digital polymerase chain reaction (ddPCR) has been used effectively in detecting mutations in formalin-fixed, paraffin-embedded (FFPE) samples of various cancer types. In this study, we assess the diagnostic utility of ddPCR to detect CTNNB1 mutations in DF with β-catenin expression on immunohistochemistry (IHC), as well as in diagnostically challenging cases. Of the 28 DFs with nuclear β-catenin expression by IHC, 24 cases showed a CTNNB1 mutation by ddPCR using primers against the most common point mutations in CTNNB1 . The most frequent mutation was T41A (n=14; 50%), followed by S45F (n=8; 33%) and S45P (n=3;12%). We identified 8 additional (myo)fibroblastic lesions of uncertain classification, which were negative for nuclear β-catenin expression by IHC. We detected CTNNB1 mutations in 3 unknown lesions, including S45F (n=2) and S45P (n=1). ddPCR is a sensitive, rapid and cost-efficient methodology to detect common CTNNB1 mutations in DF, especially in diagnostically challenging cases.

Lynch Syndrome: A Single Hereditary Cancer Syndrome or Multiple Syndromes Defined by Different Mismatch Repair Genes?

Superficial fibromas are a group of mesenchymal spindle cell lesions with pathomorphological heterogeneity and diverse molecular backgrounds. In part, they may be indicators of an underlying syndrome. Among the best-known entities of superficial fibromas is Gardner fibroma, a plaque-like benign tumor, which is associated with APC germline mutations and occurs in patients with familial adenomatosis polyposis (Gardner syndrome). Affected patients also have an increased risk to develop desmoid fibromatosis (DTF), a locally aggressive neoplasm of the deep soft tissue highly prone to local recurrences. Although a minority of DTFs occur in the syndromic context and harbor APC germline mutations, most frequently their underlying molecular aberration is a sporadic mutation in Exon 3 of the CTNNB1 gene. Up to date, a non-syndromic equivalent to Gardner fibroma carrying a CTNNB1 mutation has not been defined. Here, we present two cases of (sub-)cutaneous tumors with a hypocellular and collagen-rich Gardner fibroma-like appearance and pathogenic, somatic CTNNB1 mutations. We aim to differentiate these tumors from other fibromas according to their histological appearance, immunohistochemical staining profile and underlying somatic CTNNB1 mutations. Furthermore, we distinguish them from locally aggressive desmoid fibromatosis regarding their biological behavior, prognosis and indicated therapeutic strategies. Consequently, we call them CTNNB1-mutated superficial fibromas as a sporadic counterpart lesion to syndromic Gardner fibromas.