Clinical effectiveness and safety of olaparib in BRCA-mutated, HER2-negative metastatic breast cancer in a real-world setting: final analysis of LUCY

PURPOSE

The interim analysis of the phase IIIb LUCY trial demonstrated the clinical effectiveness of olaparib in patients with germline BRCA-mutated (gBRCAm), human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (mBC), with median progression-free survival (PFS) of 8.11 months, which was similar to that in the olaparib arm of the phase III OlympiAD trial (7.03 months). This prespecified analysis provides final overall survival (OS) and safety data.

METHODS

The open-label, single-arm LUCY trial of olaparib (300 mg, twice daily) enrolled adults with gBRCAm or somatic BRCA-mutated (sBRCAm), HER2-negative mBC. Patients had previously received a taxane or anthracycline for neoadjuvant/adjuvant or metastatic disease and up to two lines of chemotherapy for mBC.

RESULTS

Of 563 patients screened, 256 (gBRCAm, n = 253; sBRCAm, n = 3) were enrolled. In the gBRCAm cohort, median investigator-assessed PFS (primary endpoint) was 8.18 months and median OS was 24.94 months. Olaparib was clinically effective in all prespecified subgroups: hormone receptor status, previous chemotherapy for mBC, previous platinum-based chemotherapy (including by line of therapy), and previous cyclin-dependent kinase 4/6 inhibitor use. The most frequent treatment-emergent adverse events (TEAEs) were nausea (55.3%) and anemia (39.2%). Few patients (6.3%) discontinued olaparib owing to a TEAE. No deaths associated with AEs occurred during the study treatment or 30-day follow-up.

CONCLUSION

The LUCY patient population reflects a real-world population in line with the licensed indication of olaparib in mBC. These findings support the clinical effectiveness and safety of olaparib in patients with gBRCAm, HER2-negative mBC.

CLINICAL TRIAL REGISTRATION

Clinical trials registration number: NCT03286842.

From diagnosis of colorectal cancer to diagnosis of Lynch syndrome: The RM Partners quality improvement project

AIM

The UK National Institute for Health and Care Excellence guideline DG27 recommends universal testing for Lynch syndrome (LS) in all newly diagnosed colorectal cancer (CRC) patients. However, DG27 guideline implementation varies significantly by geography. This quality improvement project (QIP) was developed to measure variation and deliver an effective diagnostic pathway from diagnosis of CRC to diagnosis of LS within the RM Partners (RMP) West London cancer alliance.

METHOD

RM Partners includes a population of 4 million people and incorporates nine CRC multidisciplinary teams (MDTs), overseen by a Pathway Group, and three regional genetic services, managing approximately 1500 new CRC cases annually. A responsible LS champion was nominated within each MDT. A regional project manager and nurse practitioner were appointed to support the LS champions, to develop online training packages and patient consultation workshops. MDTs were supported to develop an 'in-house' mainstreaming service to offer genetic testing in their routine oncology clinics. Baseline data were collected through completion of the LS pathway audit of the testing pathway in 30 consecutive CRC patients from each CRC MDT, with measurement of each step of the testing pathway. Areas for improvement in each MDT were identified, delivered by the local champion and supported by the project team.

RESULTS

Overall, QIP measurables improved following the intervention. The Wilcoxon signed rank test revealed significant differences with strong effect sizes on the percentile of CRC cases undergoing mismatch repair (MMR) testing in endoscopic biopsies (p = 0.008), further testing with either methylation or BRAF V600E (p = 0/03) and in effective referral for genetic testing (from 10% to 74%; p = 0.02). During the QIP new mainstreaming services were developed, alongside the implementation of systematic and robust testing pathways. These pathways were tailored to the needs of each CRC team to ensure that patients with a diagnosis of CRC had access to testing for LS. Online training packages were produced which remain freely accessible for CRC teams across the UK.

CONCLUSION

The LS project was completed by April 2022. We have implemented a systematic approach with workforce transformation to facilitate identification and 'mainstreamed' genetic diagnosis of LS. This work has contributed to the development of a National LS Transformation Project in England which recommends local leadership within cancer teams to ensure delivery of diagnosis of LS and integration of genomics into clinical practice.

Mainstreaming of genomics in oncology: a nationwide survey of the genomics training needs of UK oncologists

OBJECTIVE

Genomics is rapidly changing treatment paradigms for cancers, obligating oncologists to have good genomics knowledge. Through this survey, we aimed to assess the current understanding of cancer genomics among UK oncologists.

METHODS

We conducted a web-based nation-wide self-assessment survey of the cancer genomics knowledge of UK clinical and medical oncology trainees and consultants.

RESULTS

In total, 150 oncologists (81 consultants and 69 trainees) responded, representing 10% of UK oncologists.Formal training in genomics had not been received by 38.7% of oncologists and 92.7% identified a need for additional genomics training.In total, 71.3% self-reported to have good knowledge of defining somatic and germline mutations, falling to 35.3% for understanding principles of gene expression and regulation. Knowledge of cancer-predisposing syndromes was highest for Lynch syndrome (40.7% good knowledge) and lowest for multiple endocrine neoplasia (14.0% good knowledge).Overall, 49.0% of respondents had consented patients for germline testing, but 80.7% reported a lack of training in genetic counselling.

CONCLUSION

Large knowledge gaps have been identified through this survey, highlighting the need for incorporation of improved formal training in cancer genomics for consultants and trainees, with an aim to equip oncologists for advances in clinical practice and to take up genetic mainstreaming confidently.

Does mainstream BRCA testing affect surgical decision-making in newly-diagnosed breast cancer patients?

BACKGROUND

Germline pathogenic variants mutations) in the BRCA1 and BRCA2 genes cause an increased risk of breast cancer and ovarian cancer. Mainstream cancer genetic testing (MCG) was introduced for breast cancer patients in our unit in 2013. Non-geneticist clinicians have been trained to offer genetic testing during initial treatment planning. We assessed the impact of timely test results on surgical decision-making.

METHODS

Women who had undergone mainstream genetic testing for breast cancer between September 2013 and September 2018 were identified from a prospective database. Surgical data were collected retrospectively.

RESULTS

580 eligible women had mainstream genetic testing. For 474 this was their first breast cancer diagnosis. The median age was 46 years (interquartile range (IQR) 38-57). The indications were: age ≤45 years for 233 (49%); triple negative disease for 192 women (40.5%); bilateral breast cancer age <60 for 39 (8%) and other for 72 (14%) women. The median time for test initiation to result was 18 days (IQR 15-21). 302 (64% received results before surgery. 88% of those found to have a BRCA mutation before surgery opted for bilateral mastectomy (compared to 5% with BRCA wild type). An additional 106 patients had a new diagnosis on a background of previous treatment. Of these all with a pathogenic variant chose bilateral mastectomy.

CONCLUSION

Timely BRCA gene testing influences surgeons' and patients' choice of surgery. It reassures women with a negative result and allows those with a positive result to take an active decision about the management of their future risk.

A digital pathway for genetic testing in UK NHS patients with cancer: BRCA-DIRECT randomised study internal pilot

BACKGROUND

Germline genetic testing affords multiple opportunities for women with breast cancer, however, current UK NHS models for delivery of germline genetic testing are clinician-intensive and only a minority of breast cancer cases access testing.

METHODS

We designed a rapid, digital pathway, supported by a genetics specialist hotline, for delivery of germline testing of BRCA1/BRCA2/PALB2 (BRCA-testing), integrated into routine UK NHS breast cancer care. We piloted the pathway, as part of the larger BRCA-DIRECT study, in 130 unselected patients with breast cancer and gathered preliminary data from a randomised comparison of delivery of pretest information digitally (fully digital pathway) or via telephone consultation with a genetics professional (partially digital pathway).

RESULTS

Uptake of genetic testing was 98.4%, with good satisfaction reported for both the fully and partially digital pathways. Similar outcomes were observed in both arms regarding patient knowledge score and anxiety, with <5% of patients contacting the genetics specialist hotline. All progression criteria established for continuation of the study were met.

CONCLUSION

Pilot data indicate preliminary demonstration of feasibility and acceptability of a fully digital pathway for BRCA-testing and support proceeding to a full powered study for evaluation of non-inferiority of the fully digital pathway, detailed quantitative assessment of outcomes and operational economic analyses.

TRIAL REGISTRATION NUMBER

ISRCTN87845055.

Copy number variants as modifiers of breast cancer risk for BRCA1/BRCA2 pathogenic variant carriers

The contribution of germline copy number variants (CNVs) to risk of developing cancer in individuals with pathogenic BRCA1 or BRCA2 variants remains relatively unknown. We conducted the largest genome-wide analysis of CNVs in 15,342 BRCA1 and 10,740 BRCA2 pathogenic variant carriers. We used these results to prioritise a candidate breast cancer risk-modifier gene for laboratory analysis and biological validation. Notably, the HR for deletions in BRCA1 suggested an elevated breast cancer risk estimate (hazard ratio (HR) = 1.21), 95% confidence interval (95% CI = 1.09-1.35) compared with non-CNV pathogenic variants. In contrast, deletions overlapping SULT1A1 suggested a decreased breast cancer risk (HR = 0.73, 95% CI 0.59-0.91) in BRCA1 pathogenic variant carriers. Functional analyses of SULT1A1 showed that reduced mRNA expression in pathogenic BRCA1 variant cells was associated with reduced cellular proliferation and reduced DNA damage after treatment with DNA damaging agents. These data provide evidence that deleterious variants in BRCA1 plus SULT1A1 deletions contribute to variable breast cancer risk in BRCA1 carriers.

Germline BRCA1 and BRCA2 testing for breast cancer survivors

Background For patients with early breast cancer, knowledge of germline BRCA1/2 status increasingly influences management as well as informing future cancer risk for patients and their families. As access to germline testing expands, it is important that this benefit is extended to survivors as well as to the newly diagnosed. Methods In collaboration with our breast unit colleagues and by embedding a Senior Genetic Counsellor in the virtual multidisciplinary meeting, we identified patients suitable for genetics review 5 years after their breast cancer diagnosis. Results Between May 2015 and December 2018, 2044 patients were discussed, of whom 769 patients were identified for notes review by Genetics. Of these, 275 had already undergone testing and 47 had confirmed germline pathogenic variants in BRCA1/2 A further 463 were recommended for referral. One hundred and eighty patients were subsequently offered testing with 161 accepting (161/180, 89%). Nine patients were found to harbour pathogenic variants in either BRCA1 or BRCA2 (9/161, 6%). Of the initial 2044 patients reviewed, 2.7% (56/2044) are now known to carry germline pathogenic variants. Conclusion The survivorship setting provides an opportunity for genetic review underpinned by collaborative working between cancer specialists and the genetics team.

Evaluation of Cancer-Based Criteria for Use in Mainstream BRCA1 and BRCA2 Genetic Testing in Patients With Breast Cancer

IMPORTANCE

Increasing BRCA1 and BRCA2 (collectively termed herein as BRCA) gene testing is required to improve cancer management and prevent BRCA-related cancers.

OBJECTIVE

To evaluate mainstream genetic testing using cancer-based criteria in patients with cancer.

DESIGN, SETTING, AND PARTICIPANTS

A quality improvement study and cost-effectiveness analysis of different BRCA testing selection criteria and access procedures to evaluate feasibility, acceptability, and mutation detection performance was conducted at the Royal Marsden National Health Service Foundation Trust as part of the Mainstreaming Cancer Genetics (MCG) Programme. Participants included 1184 patients with cancer who were undergoing genetic testing between September 1, 2013, and February 28, 2017.

MAIN OUTCOMES AND MEASURES

Mutation rates, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios were the primary outcomes.

RESULTS

Of the 1184 patients (1158 women [97.8%]) meeting simple cancer-based criteria, 117 had a BRCA mutation (9.9%). The mutation rate was similar in retrospective United Kingdom (10.2% [235 of 2294]) and prospective Malaysian (9.7% [103 of 1061]) breast cancer studies. If traditional family history criteria had been used, more than 50% of the mutation-positive individuals would have been missed. Of the 117 mutation-positive individuals, 115 people (98.3%) attended their genetics appointment and cascade to relatives is underway in all appropriate families (85 of 85). Combining with the equivalent ovarian cancer study provides 5 simple cancer-based criteria for BRCA testing with a 10% mutation rate: (1) ovarian cancer; (2) breast cancer diagnosed when patients are 45 years or younger; (3) 2 primary breast cancers, both diagnosed when patients are 60 years or younger; (4) triple-negative breast cancer; and (5) male breast cancer. A sixth criterion-breast cancer plus a parent, sibling, or child with any of the other criteria-can be added to address family history. Criteria 1 through 5 are considered the MCG criteria, and criteria 1 through 6 are considered the MCGplus criteria. Testing using MCG or MCGplus criteria is cost-effective with cost-effectiveness ratios of $1330 per discounted QALYs and $1225 per discounted QALYs, respectively, and appears to lead to cancer and mortality reductions (MCG: 804 cancers, 161 deaths; MCGplus: 1020 cancers, 204 deaths per year over 50 years). Use of MCG or MCGplus criteria might allow detection of all BRCA mutations in patients with breast cancer in the United Kingdom through testing one-third of patients. Feedback questionnaires from 259 patients and 23 cancer team members (12 oncologists, 8 surgeons, and 3 nurse specialists) showed acceptability of the process with 100% of patients pleased they had genetic testing and 100% of cancer team members confident to approve patients for genetic testing. Use of MCGplus criteria also appeared to be time and resource efficient, requiring 95% fewer genetic consultations than the traditional process.

CONCLUSIONS AND RELEVANCE

This study suggests that mainstream testing using simple, cancer-based criteria might be able to efficiently deliver consistent, cost-effective, patient-centered BRCA testing.

An Association of Cancer Physicians' strategy for improving services and outcomes for cancer patients

The Association of Cancer Physicians in the United Kingdom has developed a strategy to improve outcomes for cancer patients and identified the goals and commitments of the Association and its members.

Germline mutations affecting the proofreading domains of POLE and POLD1 predispose to colorectal adenomas and carcinomas

Many individuals with multiple or large colorectal adenomas or early-onset colorectal cancer (CRC) have no detectable germline mutations in the known cancer predisposition genes. Using whole-genome sequencing, supplemented by linkage and association analysis, we identified specific heterozygous POLE or POLD1 germline variants in several multiple-adenoma and/or CRC cases but in no controls. The variants associated with susceptibility, POLE p.Leu424Val and POLD1 p.Ser478Asn, have high penetrance, and POLD1 mutation was also associated with endometrial cancer predisposition. The mutations map to equivalent sites in the proofreading (exonuclease) domain of DNA polymerases ɛ and δ and are predicted to cause a defect in the correction of mispaired bases inserted during DNA replication. In agreement with this prediction, the tumors from mutation carriers were microsatellite stable but tended to acquire base substitution mutations, as confirmed by yeast functional assays. Further analysis of published data showed that the recently described group of hypermutant, microsatellite-stable CRCs is likely to be caused by somatic POLE mutations affecting the exonuclease domain.

Update on first-line treatment of advanced ovarian carcinoma

Despite the high response rate to first-line treatment of advanced ovarian cancer, the vast majority of patients relapse. Maximal debulking surgery and chemotherapy with a platinum doublet have remained the standard of care for many years and new approaches are imperative. Recent clinical trials have given grounds for hope. Neoadjuvant chemotherapy, intraperitoneal delivery, and dose-dense strategies have all shown promising results, as has the targeting of angiogenesis. A greater understanding of the molecular landscape of ovarian cancer is helping to identify new treatment options. In this review, we will highlight the key trials and recent progress in these areas.

A shift in the treatment of hormone receptor and human epidermal growth factor receptor 2-positive metastatic breast cancer

Historically, postmenopausal women with estrogen receptor (ER)-positive metastatic breast cancer (MBC) with a long disease-free interval and small volume disease have received an aromatase inhibitor. However, the advent of human epidermal growth factor receptor 2 (HER2) testing and its recognition as a poor prognostic indicator has led to the first line use of anti-HER2 directed therapy in combination with chemotherapy. The optimal treatment for those who are both hormone receptor and HER2 receptor positive is less clear. Tumors rich in ER are considered to be less responsive to chemotherapy, and hormone therapy has the benefit of being less toxic than chemotherapy. However, preclinical evidence suggests that HER2 overexpression may confer resistance to endocrine therapy, even in the presence of hormone receptors, due to crosstalk between the two pathways. This review summarizes the evidence from three clinical trials for combining endocrine therapy with anti-HER2 therapy in MBC. The trials raise the possibility of a new treatment approach to co-positive tumors in patients with good performance status and low tumor burden, and a means to potentially delay the need for chemotherapy.

Refinement of the basis and impact of common 11q23.1 variation to the risk of developing colorectal cancer

The common single-nucleotide polymorphism (SNP) rs3802842 at 11q23.1 has recently been reported to be associated with risk of colorectal cancer (CRC). To examine this association in detail we genotyped rs3802842 in eight independent case-control series comprising a total of 10 638 cases and 10 457 healthy individuals. A significant association between the C allele of rs3802842 and CRC risk was found (per allele OR = 1.17; 95% confidence interval [CI]: 1.12-1.22; P = 1.08 x 10(-12)) with the risk allele more frequent in rectal than colonic disease (P = 0.02). In combination with 8q21, 8q24, 10p14, 11q, 15q13.3 and 18q21 variants, the risk of CRC increases with an increasing numbers of variant alleles for the six loci (OR(per allele) = 1.19; 95% CI: 1.15-1.23; P(trend) = 7.4 x 10(-24)). Using the data from our genome-wide association study of CRC, LD mapping and imputation, we were able to refine the location of the causal locus to a 60 kb region and screened for coding changes. The absence of exonic mutations in any of the transcripts (FLJ45803, LOC120376, C11orf53 and POU2AF1) mapping to this region makes the association likely to be a consequence of non-coding effects on gene expression.

Deciphering the genetics of hereditary non-syndromic colorectal cancer

Previously we have localized to chromosome 3q21-q24, a predisposition locus for colorectal cancer (CRC), through a genome-wide linkage screen (GWLS) of 69 families without familial adenomatous polyposis or hereditary non-polyposis CRC. To further investigate Mendelian susceptibility to CRC, we extended our screen to include a further GWLS of an additional 34 CRC families. We also searched for a disease gene at 3q21-q24 by linkage disequilibrium mapping in 620 familial CRC cases and 960 controls by genotyping 1676 tagging SNPs and sequencing 30 candidate genes from the region. Linkage analysis was conducted using the Affymetrix 10K SNP array. Data from both GWLSs were pooled and multipoint linkage statistics computed. The maximum NPL score (3.01; P=0.0013) across all families was at 3q22, maximal evidence for linkage coming from families segregating rectal CRC. The same genomic position also yielded the highest multipoint heterogeneity LOD (HLOD) score under a dominant model (HLOD=2.79; P=0.00034), with an estimated 43% of families linked. In the case-control analysis, the strongest association was obtained at rs698675 (P=0.0029), but this was not significant after adjusting for multiple testing. Analysis of candidate gene mapping to the region of maximal linkage on 3q22 failed to identify a causal mutation. There was no evidence for linkage to the previously reported 9q CRC locus (NPL=0.95, P=0.23; HLOD(dominant)=0.40, HLOD(recessive)=0.20). Our findings are consistent with the hypothesis that variation at 3q22 contributes to the risk of CRC, but this is unlikely to be mediated through a restricted set of alleles.

A genome-wide association study identifies colorectal cancer susceptibility loci on chromosomes 10p14 and 8q23.3

To identify colorectal cancer (CRC) susceptibility alleles, we conducted a genome-wide association study. In phase 1, we genotyped 550,163 tagSNPs in 940 familial colorectal tumor cases (627 CRC, 313 high-risk adenoma) and 965 controls. In phase 2, we genotyped 42,708 selected SNPs in 2,873 CRC cases and 2,871 controls. In phase 3, we evaluated 11 SNPs showing association at P < 10(-4) in a joint analysis of phases 1 and 2 in 4,287 CRC cases and 3,743 controls. Two SNPs were taken forward to phase 4 genotyping (10,731 CRC cases and 10,961 controls from eight centers). In addition to the previously reported 8q24, 15q13 and 18q21 CRC risk loci, we identified two previously unreported associations: rs10795668, located at 10p14 (P = 2.5 x 10(-13) overall; P = 6.9 x 10(-12) replication), and rs16892766, at 8q23.3 (P = 3.3 x 10(-18) overall; P = 9.6 x 10(-17) replication), which tags a plausible causative gene, EIF3H. These data provide further evidence for the 'common-disease common-variant' model of CRC predisposition.

Genome-wide association scan identifies a colorectal cancer susceptibility locus on 11q23 and replicates risk loci at 8q24 and 18q21

In a genome-wide association study to identify loci associated with colorectal cancer (CRC) risk, we genotyped 555,510 SNPs in 1,012 early-onset Scottish CRC cases and 1,012 controls (phase 1). In phase 2, we genotyped the 15,008 highest-ranked SNPs in 2,057 Scottish cases and 2,111 controls. We then genotyped the five highest-ranked SNPs from the joint phase 1 and 2 analysis in 14,500 cases and 13,294 controls from seven populations, and identified a previously unreported association, rs3802842 on 11q23 (OR = 1.1; P = 5.8 x 10(-10)), showing population differences in risk. We also replicated and fine-mapped associations at 8q24 (rs7014346; OR = 1.19; P = 8.6 x 10(-26)) and 18q21 (rs4939827; OR = 1.2; P = 7.8 x 10(-28)). Risk was greater for rectal than for colon cancer for rs3802842 (P < 0.008) and rs4939827 (P < 0.009). Carrying all six possible risk alleles yielded OR = 2.6 (95% CI = 1.75-3.89) for CRC. These findings extend our understanding of the role of common genetic variation in CRC etiology.

A genome-wide association scan of tag SNPs identifies a susceptibility variant for colorectal cancer at 8q24.21

Much of the variation in inherited risk of colorectal cancer (CRC) is probably due to combinations of common low risk variants. We conducted a genome-wide association study of 550,000 tag SNPs in 930 familial colorectal tumor cases and 960 controls. The most strongly associated SNP (P = 1.72 x 10(-7), allelic test) was rs6983267 at 8q24.21. To validate this finding, we genotyped rs6983267 in three additional CRC case-control series (4,361 affected individuals and 3,752 controls; 1,901 affected individuals and 1,079 controls; 1,072 affected individuals and 415 controls) and replicated the association, providing P = 1.27 x 10(-14) (allelic test) overall, with odds ratios (ORs) of 1.27 (95% confidence interval (c.i.): 1.16-1.39) and 1.47 (95% c.i.: 1.34-1.62) for heterozygotes and rare homozygotes, respectively. Analyses based on 1,477 individuals with colorectal adenoma and 2,136 controls suggest that susceptibility to CRC is mediated through development of adenomas (OR = 1.21, 95% c.i.: 1.10-1.34; P = 6.89 x 10(-5)). These data show that common, low-penetrance susceptibility alleles predispose to colorectal neoplasia.

Evidence for a colorectal cancer susceptibility locus on chromosome 3q21-q24 from a high-density SNP genome-wide linkage scan

To identify a novel susceptibility gene for colorectal cancer (CRC), we conducted a genome-wide linkage analysis of 69 pedigrees segregating colorectal neoplasia in which involvement of known loci had been excluded, using a high-density single nucleotide polymorphism (SNP) array containing 10,204 markers. Multipoint linkage analyses were undertaken using both non-parametric (model-free) and parametric (model-based) methods. After the removal of SNPs in strong linkage disequilibrium, we obtained a maximum non-parametric linkage statistic of 3.40 (P=0.0003) at chromosomal region 3q21-q24. The same genomic position also yielded the highest multipoint heterogeneity LOD (HLOD) score under a dominant model (HLOD=3.10, genome-wide P=0.038) with 62% of families linked to the locus. We provide evidence for a novel CRC susceptibility gene. Further studies are needed to confirm this localization and to evaluate the contribution of this locus to disease incidence.

CDC4 mutations occur in a subset of colorectal cancers but are not predicted to cause loss of function and are not associated with chromosomal instability

CDC4/FBXW7 is part of a ubiquitin ligase complex which targets molecules such as cyclin E, c-myc, and c-jun for destruction. CDC4 mutations occur in several cancer types and are best described in colorectal tumors. Knockout of CDC4 in vitro in colorectal cancer cells causes changes suggestive of chromosomal instability (CIN). In p53(+/-) mice, radiation-induced lymphomas show deletion or mutation of one copy of CDC4 and knockdown of CDC4 leads to increased aneuploidy in mouse fibroblasts. We screened 244 colorectal tumors and 40 cell lines for CDC4 mutations and allelic loss. Six percent (18 of 284) of tumors, including near-diploid (CIN-) lesions, harbored CDC4 mutations and there was no association between mutation and CIN (polyploidy). The CDC4 mutation spectrum in colorectal tumors was heavily biased towards C:G > T:A changes, either missense mutations at critical arginine residues or nonsense changes in the 5' half of the gene. The reasons for this odd mutation spectrum were unclear but C:G > T:A changes were not found more often than expected at APC, K-ras, or p53 in the same tumors and we found no specific defects in DNA repair to account for the observations. No colorectal tumor was found to carry two CDC4 mutations predicted to abolish protein function; partial loss of CDC4 function may therefore cause tumorigenesis. The in vitro studies, therefore, did not assess the functional effects of mutant alleles which are found in vivo. CDC4 mutations may be selected primarily to drive progression through the cell cycle although CIN might be an important secondary effect in some cancers.

Refining molecular analysis in the pathways of colorectal carcinogenesis

BACKGROUND & AIMS

In the stepwise model, specific genetic and epigenetic changes accumulate as colorectal adenomas progress to carcinomas (CRCs). CRCs also acquire global phenotypes, particularly microsatellite instability (MSI) and aneuploidy/polyploidy (chromosomal instability, CIN). Few changes specific to MSI-low or CIN+ cancers have been established.

METHODS

We investigated 100 CRCs for: mutations and loss of heterozygosity (LOH) where appropriate, of APC, K-ras, BRAF, SMAD4, and p53; deletion on 5q around APC and 18q around SMAD4; total chromosomal-scale losses and gains; MSI; and CIN.

RESULTS

As expected, CIN- cancers had fewer chromosomal changes overall than CIN+ lesions, but after correcting for this, 5q deletions alone predicted CIN+ status. 5q deletions were not, however, significantly associated with APC mutations, which were equally frequent in CIN+ and CIN- tumors. We therefore found no evidence to show that mutant APC promotes CIN. p53 mutations/LOH were more common in CIN+ than CIN- lesions, and all chromosomal amplifications were in CIN+ tumors. CIN- cancers could be subdivided according to the total number of chromosomal-scale changes into CIN-low and CIN-stable groups; 18q deletion was the best predictor, being present in nearly all CIN-low lesions and almost no CIN-stable tumors. MSI-low was not associated with CIN, any specific mutation, a mutational signature, or clinicopathologic characteristic.

CONCLUSIONS

Overall, the components of the stepwise model (APC, K-ras, and p53 mutations, plus 18q LOH) tended to co-occur randomly. We propose an updated version of this model comprising 4 pathways of CRC pathogenesis, on the basis of 5q/18q deletions, MSI (high/low), and CIN (high/low/stable).

An update on the genetics of colorectal cancer

Colorectal carcinoma (CRC) remains a frequent cause of cancer-associated mortality in the UK and still has a relatively poor outcome. Single gene defects account for up to 2-6% of cases, but twin studies suggest a hereditary component in 35%. CRC represents a paradigm for cancer genetics. Almost all the major-gene influences on CRC have been identified, and the identification of the remaining susceptibility alleles is proving troublesome. Only a few low-penetrance alleles, such as methylene tetrahydrofolate reductase C677T, appear convincingly to be associated with CRC risk. To identify the remaining CRC genes, parallel approaches, including strategies based on linkage and association and complementary analyses such as searches for modifier genes, must be employed. To gain sufficient evidence to prove that a gene is involved in CRC predisposition, it is probably necessary for multiple, adequately-powered studies to demonstrate an association with the disease, especially if the allelic variants have only a small differential effect on risk. It may also be possible to show how genes interact with each other and the environment, although this will be even more difficult. Accurate quantitation of the allele-specific risks in different populations will be necessary, but problematic, especially if those risks combine in a fashion which is not of a straightforward additive or multiplicative type. Without any good prior evidence of the nature of the remaining genetic influence on CRC, the possibility remains that this is a truly polygenic trait or that multiple, rare variants contribute to the increased risk; in these cases, identification of the genes involved will be very difficult. Despite these potential problems, the effectiveness of preventive measures for CRC, especially in high-risk individuals, means that the search for new predisposition genes is justified.