Incidences of colorectal adenomas and cancers under colonoscopy surveillance suggest an accelerated "Big Bang" pathway to CRC in three of the four Lynch syndromes.

BACKGROUND: Colorectal cancers (CRCs) in the Lynch syndromes have been assumed to emerge through an accelerated adenoma-carcinoma pathway. In this model adenomas with deficient mismatch repair have an increased probability of acquiring additional cancer driver mutation(s) resulting in more rapid progression to malignancy. If this model was accurate, the success of colonoscopy in preventing CRC would be a function of the intervals between colonoscopies and mean sojourn time of detectable adenomas. Contrary to expectations, colonoscopy did not decrease incidence of CRC in the Lynch syndromes and shorter colonoscopy intervals have not been effective in reducing CRC incidence. The prospective Lynch Syndrome Database (PLSD) was designed to examine these issues in carriers of pathogenic variants of the mis-match repair (path_MMR) genes. MATERIALS AND METHODS: We examined the CRC and colorectal adenoma incidences in 3,574 path_MLH1, path_MSH2, path_MSH6 and path_PMS2 carriers subjected to regular colonoscopy with polypectomy, and considered the results based on sojourn times and stochastic probability paradigms. RESULTS: Most of the path_MMR carriers in each genetic group had no adenomas. There was no association between incidences of CRC and the presence of adenomas. There was no CRC observed in path_PMS2 carriers. CONCLUSIONS: Colonoscopy prevented CRC in path_PMS2 carriers but not in the others. Our findings are consistent with colonoscopy surveillance blocking the adenoma-carcinoma pathway by removing identified adenomas which might otherwise become CRCs. However, in the other carriers most CRCs likely arised from dMMR cells in the crypts that have an increased mutation rate with increased stochastic chaotic probabilities for mutations. Therefore, this mechanism, that may be associated with no or only a short sojourn time of MSI tumours as adenomas, could explain the findings in our previous and current reports.

Exploring formal and informal learning opportunities during morning report: a qualitative study.

BACKGROUND: Morning reports are an essential component of physicians' daily work. Attending morning reports is prioritized by junior doctors as it provides them with an opportunity to learn diagnostic reasoning through discussion of cases. While teaching formats during morning reports have previously been reported, an in-depth analysis of what learning opportunities exist, e.g., how teaching is enacted during morning reports, is lacking. This qualitative study explores learning opportunities during morning reports. METHODS: We used an explorative design based on video-recordings of 23 morning reports from two surgical departments, an internal medicine department and an emergency department. We used thematic analysis combined with and inspired by Eraut's theoretical framework of workplace learning. RESULTS: Both formal and informal learning opportunities were identified. Formal learning opportunities had the character of planned teaching activities, and we identified four themes: (1) modes of teaching, (2) structure, (3) presenter role, and (4) participant involvement. Informal learning, on the other hand, was often implicit and reactive, while deliberate learning opportunities were rare. The data showed many missed opportunities for learning. CONCLUSION: Both formal and informal learning opportunities are present during morning reports. However, a prevalent focus on medical topics exists, leaving other important aspects of the medical role under-discussed. Pedagogical methods could be employed more optimally, and harnessing the potential of missed opportunities should be encouraged.

Practical guidelines of the EOTTD for pathological and genetic diagnosis of hydatidiform moles.

Hydatidiform moles are rare and thus most pathologists and geneticists have little experience with their diagnosis. It is important to promptly and correctly identify hydatidiform moles given that they are premalignant disorders associated with a risk of persistent gestational trophoblastic disease and gestational trophoblastic neoplasia. Improvement in diagnosis can be achieved with uniformization of diagnostic criteria and establishment of algorithms. To this aim, the Pathology and Genetics Working Party of the European Organisation for Treatment of Trophoblastic Diseases has developed guidelines that describe the pathological criteria and ancillary techniques that can be used in the differential diagnosis of hydatidiform moles. These guidelines are based on the best available evidence in the literature, professional experience and consensus of the experts' group involved in its development.

National clinical Genetic Networks - GENets - Establishment of expert collaborations in Denmark.

Genetic conditions are often familial, but not all relatives receive counseling from the same institution. It is therefore necessary to ensure consistency in variant interpretation, counseling practices, and clinical follow up across health care providers. Furthermore, as new possibilities for gene-specific treatments emerge and whole genome sequencing becomes more widely available, efficient data handling and knowledge sharing between clinical laboratory geneticists and medical specialists in clinical genetics are increasingly important. In Denmark, these needs have been addressed through the establishment of collaborative national networks called Genetic Expert Networks or "GENets". These networks have enhanced patient and family care significantly by bringing together groups of experts in national collaborations. This promotes coordinated clinical care, the dissemination of best clinical practices, and facilitates the exchange of new knowledge.

Dominantly inherited micro-satellite instable cancer - the four Lynch syndromes - an EHTG, PLSD position statement.

The recognition of dominantly inherited micro-satellite instable (MSI) cancers caused by pathogenic variants in one of the four mismatch repair (MMR) genes MSH2, MLH1, MSH6 and PMS2 has modified our understanding of carcinogenesis. Inherited loss of function variants in each of these MMR genes cause four dominantly inherited cancer syndromes with different penetrance and expressivities: the four Lynch syndromes. No person has an "average sex "or a pathogenic variant in an "average Lynch syndrome gene" and results that are not stratified by gene and sex will be valid for no one. Carcinogenesis may be a linear process from increased cellular division to localized cancer to metastasis. In addition, in the Lynch syndromes (LS) we now recognize a dynamic balance between two stochastic processes: MSI producing abnormal cells, and the host's adaptive immune system's ability to remove them. The latter may explain why colonoscopy surveillance does not reduce the incidence of colorectal cancer in LS, while it may improve the prognosis. Most early onset colon, endometrial and ovarian cancers in LS are now cured and most cancer related deaths are after subsequent cancers in other organs. Aspirin reduces the incidence of colorectal and other cancers in LS. Immunotherapy increases the host immune system's capability to destroy MSI cancers. Colonoscopy surveillance, aspirin prevention and immunotherapy represent major steps forward in personalized precision medicine to prevent and cure inherited MSI cancer.

The clinical use of polygenic risk scores.

Polygenic risk scores (PRS) identify at-risk individuals for many common diseases. A discussion of strengths and limitations is carried out in this review. PRS complement traditional genetic testing and have shown utility in establishing a proper diagnosis and guiding primary and secondary prevention. Some individuals with high PRS have risks similar to those with monogenic predisposition. Limitations include potential misinterpretations, problems with application across ancestries, and limited usefulness in low-heritability traits. Despite its shortcomings PRS are predicted to play major roles in the future of personal medicine and genetic testing.

Androgenetic/biparental mosaicism in a diploid mole-like conceptus: report of a case with triple paternal contribution.

Hydatidiform moles (HMs) are divided into two types: partial hydatidiform mole (PHM) which is most often diandric monogynic triploid and complete hydatidiform mole (CHM) which is most often diploid androgenetic. Morphological features and p57 immunostaining are routinely used to distinguish both entities. Genetic analyses are required in challenging cases to determine the parental origin of the genome and ploidy. Some gestations cannot be accurately classified however. We report a case with atypical pathologic and genetic findings that correspond neither to CHM nor to PHM. Two populations of villi with divergent and discordant p57 expression were observed: morphologically normal p57 + villi and molar-like p57 discordant villi with p57 + stromal cells and p57 - cytotrophoblasts. Genotyping of DNA extracted from microdissected villi demonstrated that the conceptus was an androgenetic/biparental mosaic, originating from a zygote with triple paternal contribution, and that only the p57 - cytotrophoblasts were purely androgenetic, increasing the risk of neoplastic transformation.

Whole genome sequencing and disease pattern in patients with juvenile polyposis syndrome: a nationwide study.

Juvenile polyposis syndrome (JPS) is a hereditary hamartomatous polyposis syndrome characterized by gastrointestinal juvenile polyps and increased risk of gastrointestinal cancer. Germline pathogenic variants are detected in SMAD4 or BMPR1A, however in a significant number of patients with JPS, the etiology is unknown. From Danish registers, and genetic department and laboratories, we identified all patients in Denmark with a clinical diagnosis of JPS and/or a pathogenic variant in BMPR1A or SMAD4. In patients where no variant had been detected, we performed genetic analysis, including whole genome sequencing. We collected clinical information on all patients to investigate the phenotypic spectrum. Sixty-six patients (mean age 40 years) were included of whom the pathogenic variant was unknown in seven patients. We detected a pathogenic variant in SMAD4 or PTEN in additional three patients and thus ≈ 95% of patients had a pathogenic germline variant. Endoscopic information was available in fifty-two patients (79%) and of these 31 (60%) fulfilled the clinical criteria of JPS. In 41 patients (79%), other types of polyps than juvenile had been removed. Our results suggest that almost all patients with a clinical diagnosis of JPS has a pathogenic variant in mainly BMPR1A, SMAD4, and more rarely PTEN. However, not all patients with a pathogenic variant fulfil the clinical criteria of JPS. We also demonstrated a wide clinical spectrum, and that the histopathology of removed polyps varied.

How doctors build community and socialize into a clinical department through morning reports. A positioning theory study.

PHENOMENON: The morning report is one of the longest surviving hospital practices. Most studies of the morning report focus on the effectiveness of formal medical training, while focus on social and communicative aspects is rarer. This study explores the social interactions and communication in morning reports, examining the ways in which they contribute to the construction of professional identity and socialization into the community of the clinical department. APPROACH: We used a qualitative explorative design with video observations of morning reports. Our data consisted of 43 video-recorded observations (in all, 15.5 hours) from four different hospital departments in Denmark. These were analyzed using the theoretical framework of positioning theory. FINDINGS: A key finding was that each department followed its own individual structure. This order was not articulated as such but played out implictly. Two alternative storylines unfolded in the elements of the morning report: 1) being equal members of the specialty and department, and 2) preserving the hierarchical community and its inherent positions. INSIGHTS: The morning report can be seen as playing an important role in community making. It unfolds as a "dance" of repeated elements in a complex collegial space. Within this complexity, the morning report is a space for positioning oneself and others as a collegial "we", i.e., equal members of a department and specialty, at the same time as "having a place" in a hierarchal community. Thus, morning reports contribute to developing professional identity and socialization into the medical community.

When to consult a geneticist specialising in gestational trophoblastic disease.

BACKGROUND: Gestational trophoblastic disease comprises hydatidiform moles and a rare group of malignancies that derive from trophoblasts. Although there are typical morphological features that may distinguish hydatidiform moles from non-molar products of conception, such features are not always present, especially at early stages of pregnancy. Furthermore, mosaic/chimeric pregnancies and twin pregnancies make pathological diagnosis challenging while trophoblastic tumours can also pose diagnostic problems in terms of their gestational or non-gestational origin. OBJECTIVES: To show that ancillary genetic testing can be used to aid diagnosis and clinical management of GTD. METHODS: Each author identified cases where genetic testing, including short tandem repeat (STR) genotyping, ploidy analysis, next generation sequencing and immunostaining for p57, the product of the imprinted gene CDKN1C, facilitated accurate diagnosis and improved patient management. Representative cases were chosen to illustrate the value of ancillary genetic testing in different scenarios. OUTCOME: Genetic analysis of placental tissue can aid in determining the risk of developing gestational trophoblastic neoplasia, facilitating discrimination between low risk triploid (partial) and high risk androgenetic (complete) moles, discriminating between a hydatidiform mole twinned with a normal conceptus and a triploid conception and identification of androgenetic/biparental diploid mosaicism. STR genotyping of placental tissue and targeted gene sequencing of patients can identify women with an inherited predisposition to recurrent molar pregnancies. Genotyping can distinguish gestational from non-gestational trophoblastic tumours using tissue or circulating tumour DNA, and can also identify the causative pregnancy which is the key prognostic factor for placental site and epithelioid trophoblastic tumours. CONCLUSIONS AND OUTLOOK: STR genotyping and P57 immunostaining have been invaluable to the management of gestational trophoblastic disease in many situations. The use of next generation sequencing and of liquid biopsies are opening up new pathways for GTD diagnostics. Development of these techniques has the potential to identify novel biomarkers of GTD and further refine diagnosis.

Mortality by age, gene and gender in carriers of pathogenic mismatch repair gene variants receiving surveillance for early cancer diagnosis and treatment: a report from the prospective Lynch syndrome database.

Background: The Prospective Lynch Syndrome Database (PLSD) collates information on carriers of pathogenic or likely pathogenic MMR variants (path_MMR) who are receiving medical follow-up, including colonoscopy surveillance, which aims to the achieve early diagnosis and treatment of cancers. Here we use the most recent PLSD cohort that is larger and has wider geographical representation than previous versions, allowing us to present mortality as an outcome, and median ages at cancer diagnoses for the first time. Methods: The PLSD is a prospective observational study without a control group that was designed in 2012 and updated up to October 2022. Data for 8500 carriers of path_MMR variants from 25 countries were included, providing 71,713 years of follow up. Cumulative cancer incidences at 65 years of age were combined with 10-year crude survival following cancer, to derive estimates of mortality up to 75 years of age by organ, gene, and gender. Findings: Gynaecological cancers were more frequent than colorectal cancers in path_MSH2, path_MSH6 and path_PMS2 carriers [cumulative incidence: 53.3%, 49.6% and 23.3% at 75 years, respectively]. Endometrial, colon and ovarian cancer had low mortality [8%, 13% and 15%, respectively] and prostate cancers were frequent in male path_MSH2 carriers [cumulative incidence: 39.7% at 75 years]. Pancreatic, brain, biliary tract and ureter and kidney and urinary bladder cancers were associated with high mortality [83%, 66%, 58%, 27%, and 29%, respectively]. Among path_MMR carriers undergoing colonoscopy surveillance, particularly path_MSH2 carriers, more deaths followed non-colorectal Lynch syndrome cancers than colorectal cancers. Interpretation: In path_MMR carriers undergoing colonoscopy surveillance, non-colorectal Lynch syndrome cancers were associated with more deaths than were colorectal cancers. Reducing deaths from non-colorectal cancers presents a key challenge in contemporary medical care in Lynch syndrome. Funding: We acknowledge funding from the Norwegian Cancer Society, contract 194751-2017.

Survival, surveillance, and genetics in patients with Peutz-Jeghers syndrome: A nationwide study.

Peutz-Jeghers syndrome (PJS) is an autosomal dominant hereditary polyposis syndrome causing increased morbidity and mortality due to complications of polyposis and the development of cancer. STK11 is the only gene known to be associated with PJS, although in 10%-15% of patients fulfilling the diagnostic criteria no pathogenic variant (PV) is identified. The primary aim of this study was to identify the genetic etiology in all known PJS patients in Denmark and to estimate the risk of cancer, effect of surveillance and overall survival. We identified 56 patients (2-83 years old) with PJS. The detection rate of PVs was 96%, including three cases of mosaicism (6%). In two patients a variant was not detected. At the age of 40 years, the probabilities of cancer and death were 21% and 16%, respectively; at the age of 70 years these probabilities were 71% and 69%. Most cases of cancer (92%) were identified between the scheduled examinations in the surveillance program. These observations emphasize that PJS should be regarded as a general cancer predisposition syndrome, where improvement of clinical care is needed.

Feasibility and early clinical impact of precision medicine for late-stage cancer patients in a regional public academic hospital.

AIM: Our goal was to describe a precision medicine program in a regional academic hospital, characterize features of included patients and present early data on clinical impact. MATERIALS AND METHODS: We prospectively included 163 eligible patients with late-stage cancer of any diagnosis from June 2020 to May 2022 in the Proseq Cancer trial. Molecular profiling of new or fresh frozen tumor biopsies was done by WES and RNAseq with parallel sequencing of non-tumoral DNA as individual reference. Cases were presented at a National Molecular Tumor Board (NMTB) for discussion of targeted treatment. Subsequently, patients were followed for at least 7 months. RESULTS: 80% (N = 131) of patients had a successful analysis done, disclosing at least one pathogenic or likely pathogenic variant in 96%. A strongly or potentially druggable variant was found in 19% and 73% of patients, respectively. A germline variant was identified in 2.5%. Median time from trial inclusion to NMTB decision was one month. One third (N = 44) of patients who underwent molecularly profiling were matched with a targeted treatment, however, only 16% were either treated (N = 16) or are waiting for treatment (N = 5), deteriorating performance status being the primary cause of failure. A history of cancer among 1st degree relatives, and a diagnosis of lung or prostate cancer correlated with greater chance of targeted treatment being available. The response rate of targeted treatments was 40%, the clinical benefit rate 53%, and the median time on treatment was 3.8 months. 23% of patients presented at NMTB were recommended clinical trial participation, not dependent on biomarkers. CONCLUSIONS: Precision medicine in end-stage cancer patients is feasible in a regional academic hospital but should continue within the frame of clinical protocols as few patients benefit. Close collaboration with comprehensive cancer centers ensures expert evaluations and equality in access to early clinical trials and modern treatment.

Diagnosis of hydatidiform moles using circulating gestational trophoblasts isolated from maternal blood.

INTRODUCTION: Identifying hydatidiform moles (HMs) is crucial due to the risk of gestational trophoblastic neoplasia. When a HM is suspected on clinical findings, surgical termination is recommended. However, in a substantial fraction of the cases, the conceptus is actually a non-molar miscarriage. If distinction between molar and non-molar gestations could be obtained before termination, surgical intervention could be minimized. METHODS: Circulating gestational trophoblasts (cGTs) were isolated from blood from 15 consecutive women suspected of molar pregnancies in gestational week 6-13. The trophoblasts were individually sorted using fluorescence activated cell sorting. STR analysis targeting 24 loci was performed on DNA isolated from maternal and paternal leukocytes, chorionic villi, cGTs, and cfDNA. RESULTS: With a gestational age above 10 weeks, cGTs were isolated in 87% of the cases. Two androgenetic HMs, three triploid diandric HMs, and six conceptuses with diploid biparental genome were diagnosed using cGTs. The STR profiles in cGTs were identical to the profiles in DNA from chorionic villi. Eight of the 15 women suspected to have a HM prior to termination had a conceptus with a diploid biparental genome, and thus most likely a non-molar miscarriage. DISCUSSION: Genetic analysis of cGTs is superior to identify HMs, compared to analysis of cfDNA, as it is not hampered by the presence of maternal DNA. cGTs provide information about the full genome in single cells, facilitating estimation of ploidy. This may be a step towards differentiating HMs from non-HMs before termination.

Distinct gastric phenotype in patients with pathogenic variants in SMAD4: A nationwide cross-sectional study.

Background and study aims In most patients with juvenile polyposis Syndrome, it is possible to detect a pathogenic germline variant in SMAD4 or BMPR1A . It is well known that patients with a pathogenic variant in SMAD4 have a higher risk of gastric polyposis and gastric cancer compared to BMPR1A carriers, but the natural history of gastric involvement is poorly described. We aimed to systematically review endoscopic and histopathological gastric findings in Danish patients with pathogenic variants in SMAD4. Patients and methods This was a retrospective, cross-sectional study including endoscopic and histological gastric findings in all known Danish patients with pathogenic variants in SMAD4 . The patients were identified by data from various registries as well as from clinical genetic departments and laboratories. Results We identified 41 patients (2-72 years) with a pathogenic SMAD4 variant . In 31 patients, we were able to retrieve information on upper gastrointestinal endoscopy. Eighty-seven percent had at least one gastric abnormality including erythema (72 %) and edema (72 %). Half of the patients also had vulnerability of the mucosa and 68 % had gastric polyposis. An increasing frequency of abnormalities were observed with increasing age. Gastric cancer was diagnosed in 5 % of the cases and 22 % had a gastrectomy mainly because of massive polyposis. Conclusions This study showed that most patients with pathogenic SMAD4 variants have a distinct phenotype of the gastric mucosa, and with an increasing severity in the elderly patients. These findings provide new insights into the natural history of gastric manifestations in patients with pathogenic SMAD4 variants.

Colorectal cancer incidences in Lynch syndrome: a comparison of results from the prospective lynch syndrome database and the international mismatch repair consortium.

OBJECTIVE: To compare colorectal cancer (CRC) incidences in carriers of pathogenic variants of the MMR genes in the PLSD and IMRC cohorts, of which only the former included mandatory colonoscopy surveillance for all participants. METHODS: CRC incidences were calculated in an intervention group comprising a cohort of confirmed carriers of pathogenic or likely pathogenic variants in mismatch repair genes (path_MMR) followed prospectively by the Prospective Lynch Syndrome Database (PLSD). All had colonoscopy surveillance, with polypectomy when polyps were identified. Comparison was made with a retrospective cohort reported by the International Mismatch Repair Consortium (IMRC). This comprised confirmed and inferred path_MMR carriers who were first- or second-degree relatives of Lynch syndrome probands. RESULTS: In the PLSD, 8,153 subjects had follow-up colonoscopy surveillance for a total of 67,604 years and 578 carriers had CRC diagnosed. Average cumulative incidences of CRC in path_MLH1 carriers at 70 years of age were 52% in males and 41% in females; for path_MSH2 50% and 39%; for path_MSH6 13% and 17% and for path_PMS2 11% and 8%. In contrast, in the IMRC cohort, corresponding cumulative incidences were 40% and 27%; 34% and 23%; 16% and 8% and 7% and 6%. Comparing just the European carriers in the two series gave similar findings. Numbers in the PLSD series did not allow comparisons of carriers from other continents separately. Cumulative incidences at 25 years were < 1% in all retrospective groups. CONCLUSIONS: Prospectively observed CRC incidences (PLSD) in path_MLH1 and path_MSH2 carriers undergoing colonoscopy surveillance and polypectomy were higher than in the retrospective (IMRC) series, and were not reduced in path_MSH6 carriers. These findings were the opposite to those expected. CRC point incidence before 50 years of age was reduced in path_PMS2 carriers subjected to colonoscopy, but not significantly so.

von Hippel-Lindau disease: Updated guideline for diagnosis and surveillance.

von Hippel Lindau disease (vHL) is caused by a hereditary predisposition to multiple neoplasms, especially hemangioblastomas in the retina and CNS, renal cell carcinomas (RCC), pheochromocytomas, neuroendocrine pancreatic tumours (PNET) and endolymphatic sac tumours. Evidence based approaches are needed to ensure an optimal clinical care, while minimizing the burden for the patients and their families. This guideline is based on evidence from the international vHL literature and extensive research of geno- and phenotypic characteristics, disease progression and surveillance effect in the national Danish vHL cohort. We included the views and preferences of the Danish vHL patients, ensured consensus among Danish experts and compared with international recommendations. RECOMMENDATIONS: vHL can be diagnosed on clinical criteria, only; however, in most cases the diagnosis can be supported by identification of a pathogenic or likely pathogenic variant in VHL. Surveillance should be initiated in childhood in persons with, or at risk of, vHL, and include regular examination of the retina, CNS, inner ear, kidneys, neuroendocrine glands, and pancreas. Treatment of vHL manifestations should be planned to optimize the chance of cure, without unnecessary sequelae. Most manifestations are currently treated by surgery. However, belzutifan, that targets HIF-2α was recently approved by the U.S. Food and Drug Administration (FDA) for adult patients with vHL-associated RCC, CNS hemangioblastomas, or PNETs, not requiring immediate surgery. Diagnostics, surveillance, and treatment of vHL can be undertaken successfully by experts collaborating in multidisciplinary teams. Systematic registration, collaboration with patient organisations, and research are fundamental for the continuous improvement of clinical care and optimization of outcome with minimal patient inconvenience.

Familial colorectal cancer and tooth agenesis caused by an AXIN2 variant: how do we detect families with rare cancer predisposition syndromes?

We present a three-generation family with an AXIN2 variant and a family history of colorectal cancer (CRC), colon polyps and tooth agenesis. A likely pathogenic variant was detected in the AXIN2 gene (c.1994dup; p.(Asn666Glnfs*41)). This variant has previously been associated with tooth agenesis and polyposis, only. In this case report we describe eight carriers with tooth agenesis and variable clinical findings, including polyps and CRC. Our case provides additional knowledge to the sparse data on genotype-phenotype association related to AXIN2 associated cancer syndrome. Further, our case highlights the importance of analysing an extended CRC and oligodontia/ectodermal dysplasia gene panel including AXIN2 but also raises awareness and discussion about appropriate surveillance program.

Functional megalin is expressed in renal cysts in a mouse model of adult polycystic kidney disease.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the progressive growth of cysts and a decline of renal function. The clinical feasibility of the number of potential disease-modifying drugs is limited by systemic adverse effects. We hypothesize that megalin, a multiligand endocytic receptor expressed in the proximal tubule, may be used to facilitate drug uptake into cysts, thereby allowing for greater efficacy and fewer side effects. METHODS: The cyst expression of various tubular markers, including megalin and aquaporin 2 (AQP2), was analysed by immunohistochemistry (IHC) of kidney sections from the ADPKD mouse model (PKD1RC/RC ) at different post-natal ages. The endocytic function of megalin in cysts was examined by IHC of kidney tissue from mice injected with the megalin ligand aprotinin. RESULTS: Cyst lining epithelial cells expressing megalin were observed at all ages; however, the proportion decreased with age. Concomitantly, an increasing proportion of cysts revealed expression of AQP2, partial expression of megalin and/or AQP2 or no expression of the examined markers. Endocytic uptake of aprotinin was evident in megalin-positive cysts, but only in those that remained connected to the renal tubular system. CONCLUSIONS: Megalin-expressing cysts were observed at all ages, but the proportion decreased with age, possibly due to a switch in tubular origin, a merging of cysts of different tubular origin and/or a change in the expression pattern of cyst lining cells. Megalin expressed in cysts was functional, suggesting that megalin-mediated endocytosis is a potential mechanism for drug targeting in ADPKD if initiated early in the disease.