Total Neoadjuvant Treatment for Locally Advanced Rectal Cancer Patients: Where Do We Stand?

The therapeutic landscape in locally advanced rectal cancer (LARC) has undergone a significant paradigm shift in recent years with the rising adoption of total neoadjuvant treatment (TNT). This comprehensive approach entails administering chemotherapy and radiation therapy before surgery, followed by optional adjuvant chemotherapy. To establish and deliver the optimal tailored treatment regimen to the patient, it is crucial to foster collaboration among a multidisciplinary team comprising healthcare professionals from various specialties, including medical oncology, radiation oncology, surgical oncology, radiology, and pathology. This review aims to provide insights into the current state of TNT for LARC and new emerging strategies to identify potential directions for future research and clinical practice, such as circulating tumor-DNA, immunotherapy in mismatch-repair-deficient tumors, and nonoperative management.

Universal tumor screening in a population with MSH6- and PMS2-associated Lynch syndrome.

PURPOSE: Universal screening for Lynch syndrome (LS) on resected colorectal carcinomas (CRCs) and endometrial carcinomas (ECs) was implemented in Iceland in 2017 using immunohistochemistry (IHC) for mismatch repair (MMR) proteins. We examined the efficacy of the universal screening algorithm to detect LS and the diagnostic accuracy of MMR IHC by comparing results with a population-based genotype database. METHODS: All patients diagnosed with CRC or EC per the Icelandic Cancer Registry from 2017 to 2019 who had tumor MMR IHC performed were included. Pathology reports and patient charts were reviewed. MMR IHC stains were crossmatched with genotyping results obtained from the deCODE database. RESULTS: IHC staining was done on 404 patients with CRC and 74 patients with EC. A total of 61 (15.1%) patients with CRC and 15 (20.3%) patients with EC were MMR-deficient. MMR IHC had 88.9% sensitivity in identifying patients with LS and a positive predictive value of 10.7%. Only 50% of individuals were appropriately referred for genetic testing, leading to underdiagnosis of LS. CONCLUSION: Universal screening for LS using MMR protein IHC in CRC and EC accurately identified patients appropriate for genetic testing in a population with MSH6 and PMS2 LS predominance. Because of lack of referral to genetic counseling, only 50% of patients with LS were identified through the screening algorithm.

The diversity of tumours with microsatellite instability: molecular mechanisms and impact upon microsatellite instability testing and mismatch repair protein immunohistochemistry.

Microsatellite instability (MSI) as a distinct molecular phenotype in human neoplasms was first recognised in 1993. Since then there has been tremendous progress in our understanding of this phenotype, including its genomic drivers and functional consequences. Currently, the multiple lines of investigation on MSI seem to have converged upon one important facet: its diversity, both genotypically and phenotypically, and both within and across tumour types. This review article offers a pathologist's perspective on our current understanding of this diversity, and highlights its potentially significant impact on the effective use of our current MSI detection tools: PCR- or sequencing-based MSI testing and mismatch repair protein immunohistochemistry.

Clinicopathological features of 50 mismatch repair (MMR)-deficient endometrial carcinomas, tested by immunohistochemistry: A single institutional feasibility study, India.

There are few comprehensive studies from Asia on clinicopathologic features of mismatch repair (MMR)-deficient endometrial carcinomas, including rarely from our country. One hundred and four cases of endometrial carcinomas were tested for four MMR proteins by immunohistochemistry. Among 50 MMR-deficient (MMRd) tumors(48%), age-range was 27-68 years(median = 53) and tumor size(n = 34) varied from 1.2-10 cm(average = 4.6). Lower uterine segment(LUS) was involved in 21/31 cases(67.7%). Histopathologically, all cases were endometrioid adenocarcinomas(EMACs), of FIGO grade 2(low-grade)(18 cases) and 3(high-grade)(32 cases), displaying de-differentiated, undifferentiated and lymphoepithelioma(LE)-like patterns, in 24 cases(48%). Tumor infiltration ≥ half of myometrium was seen in 30/44 cases (68.1%); lymphovascular emboli in 19/43 cases(44.1%); and lymph node metastasis in 7/22(31.8%) cases. Uncommonly, clear cell component(n = 2) and focal neuroendocrine differentiation (n = 2) were observed. Immunohistochemically, tumor cells showed paired loss of MLH1 and PMS2 in 33(66%) and MSH2 and MSH6 in 14(28%) cases, along with loss of MSH2 and PMS2, in two and a single case, respectively. Nine patients(18%) were treated for another cancer and 9/33(27.2%) disclosed familial history of cancer. MSH2 was the most frequently lost MMR protein in those cases. Additionally, tumor cells displayed ER positivity in 41/50 cases(82%), PR in 38/41cases(92.6%) and wild-type p53 staining in 24/28 cases(85.7%). Tumor with LE-pattern showed PDLI immunoexpression. Certain clinicopathologic features suggestive for MMRd associated ECs, such as relatively large-sized tumors, involving LUS; especially high-grade, infiltrative EMACs, with undifferentiated/de-differentiated, and LE-like patterns; showing deep muscle invasion, frequent PR immunoexpression and invariably, wild-type p53 immunostaining can be useful in screening cases of Lynch syndrome. This constitutes the first report on these tumors from our country.

Detection of coding microsatellite frameshift mutations in DNA mismatch repair-deficient mouse intestinal tumors.

Different DNA mismatch repair (MMR)-deficient mouse strains have been developed as models for the inherited cancer predisposing Lynch syndrome. It is completely unresolved, whether coding mononucleotide repeat (cMNR) gene mutations in these mice can contribute to intestinal tumorigenesis and whether MMR-deficient mice are a suitable molecular model of human microsatellite instability (MSI)-associated intestinal tumorigenesis. A proof-of-principle study was performed to identify mouse cMNR-harboring genes affected by insertion/deletion mutations in MSI murine intestinal tumors. Bioinformatic algorithms were developed to establish a database of mouse cMNR-harboring genes. A panel of five mouse noncoding mononucleotide markers was used for MSI classification of intestinal matched normal/tumor tissues from MMR-deficient (Mlh1(-/-) , Msh2(-/-) , Msh2(LoxP/LoxP) ) mice. cMNR frameshift mutations of candidate genes were determined by DNA fragment analysis. Murine MSI intestinal tumors but not normal tissues from MMR-deficient mice showed cMNR frameshift mutations in six candidate genes (Elavl3, Tmem107, Glis2, Sdccag1, Senp6, Rfc3). cMNRs of mouse Rfc3 and Elavl3 are conserved in type and length in their human orthologs that are known to be mutated in human MSI colorectal, endometrial and gastric cancer. We provide evidence for the utility of a mononucleotide marker panel for detection of MSI in murine tumors, the existence of cMNR instability in MSI murine tumors, the utility of mouse subspecies DNA for identification of polymorphic repeats, and repeat conservation among some orthologous human/mouse genes, two of them showing instability in human and mouse MSI intestinal tumors. MMR-deficient mice hence are a useful molecular model system for analyzing MSI intestinal carcinogenesis.

Activity of pembrolizumab and lenvatinib in mismatch repair deficient (dMMR) endometrial cancer patients who have failed pembrolizumab monotherapy: A case series.

To evaluate the efficacy of the combination of pembrolizumab and lenvatinib in MMR deficient (dMMR) endometrial cancer (EC) patients who previously failed to respond to single-agent pembrolizumab. A retrospective review of MMR deficient endometrial cancer patients was performed. Patients who failed to respond to pembrolizumab as a single-agent and subsequently received a combination of pembrolizumab and lenvatinib were analyzed. RECIST 1.1 criteria was used to establish clinical response (complete response, partial response, stable disease, and progression) based on CT and/or PET, comparing imaging before and after the addition of lenvatinib. Radiologic review was conducted by an independent radiologist. Eight patients with dMMR EC meeting treatment criteria were identified. The patients' ages ranged from 54 to 80 and all tumors identified were of endometrioid histology. Initial pathologic stage ranged from FIGO stage IB to IVB and recurrence confirmed via imaging or tissue biopsy. Patients received a median of 14 cycles of therapy with pembrolizumab and lenvatinib (range 1-39). All patients had decrease in measurable disease with an objective response of 75 % (PR 62.5 %, CR 12.5 %). Both patients who received the initial recommended dose of 20 mg daily required a dose reduction. Based on this retrospective study, patients with dMMR EC without significant benefit from pembrolizumab monotherapy have a significant clinical response after the addition of lenvatinib. Combination therapy should be considered for dMMR EC patients who fail pembrolizumab monotherapy.

Case Report: Life-threatening hypercalcemia associated with MMR-deficient endometrial carcinoma secreting parathyroid hormone.

Ectopic secretion of parathyroid hormone (PTH) is a rare cause of hypercalcemia in malignancy patients. A 56-year-old woman with life-threatening hypercalcemia was caused by poorly-differentiated endometrial carcinoma secreting PTH with concomitant nodular goiter mimic parathyroid tumors. The elevated level of PTH and calcium decreased immediately after cytoreductive surgery (CRS). The pathology confirmed mismatch repair (MMR)-deficient endometrial carcinoma with PTH expression. The patient received four-course chemotherapy and one-course immunotherapy after CRS. The disease progression led to multiple organ failure and death about five months after CRS. To our knowledge, this is the first case of hypercalcemia caused by MMR-deficient endometrial carcinoma with ectopic PTH secreting and the first report of malignancy associated hypercalcemia complicated with nodular goiter.

Extramedullary Hematopoiesis in Mismatch Repair Deficient Colon Cancer Patient on Adjuvant Chemotherapy.

A 59-year-old male presented with a two-month history of abdominal pain and was found to have an obstructing cecal mass. Colonoscopy and biopsy confirmed invasive adenocarcinoma. Immunohistochemical analyses for mismatch repair (MMR) proteins revealed the loss of MLH1 as well as PMS2 in cancerous nuclei, which makes the tumor MMR deficient. Negative germline testing for MMR proteins ruled out the Lynch syndrome. After negative staging computerized tomography scan for distant metastases, he underwent ileocolectomy with ileotransverse colonic anastomosis. Final pathological analysis revealed poorly differentiated adenocarcinoma with signet ring features, negative margins, and 3/22 lymph nodes positive, classified as stage IIIB (T4aN1bM0). Adjuvant chemotherapy with modified FOLFOX (leucovorin calcium/folinic acid, fluorouracil, and oxaliplatin) was started without the use of any growth factor support. After cycle 9 of 12, he developed mild transaminitis, carcinoembryonic antigen elevation, and interval development of two heterogeneously enhancing hepatic lesions. Biopsy of both of these lesions revealed extramedullary hematopoiesis (EMH), with no evidence of metastatic disease. He completed adjuvant chemotherapy without complication, and these liver lesions have decreased in size during the follow-up period of almost two years thus far. EMH is extremely rare in patients with colon cancer. Contributing factors include therapy-specific (growth factor support), bone marrow suppression secondary to chemotherapy and radiation therapy, and tumor-specific factors (cytokine and growth factors released by the tumor). To the best of our knowledge, this is the first case report of EMH in an MMR deficient colon cancer patient on adjuvant FOLFOX. MMR-deficient tumors show signs of a high degree of infiltration with CD8+ cytotoxic T lymphocytes as well as helper T cells, leading to increased production of cytokines, such as interferon-γ. This could be a potential etiology behind EMH in our patient who was MMR deficient. The role of the MMR-deficient state in the development of EMH should be explored further.

Long-Term Survival and Clinicopathological Implications of DNA Mismatch Repair Status in Endometrioid Endometrial Cancers in Hong Kong Chinese Women.

To investigate the role of DNA mismatch repair status (MMR) in survival of endometrioid endometrial cancer in Hong Kong Chinese women and its correlation to clinical prognostic factors, 238 patients with endometrioid endometrial cancer were included. Tumor MMR status was evaluated by immunohistochemistry. Clinical characteristics and survival were determined. Association of MMR with survival and clinicopathological parameters were assessed. MMR deficiency (dMMR) was found in 43 cases (16.5%). dMMR was associated with poor prognostic factors including older age, higher stage, higher grade, larger tumor size and more radiotherapy usage. Long-term survival was worse in dMMR compared to the MMR proficient group. The dMMR group had more deaths, shorter disease-specific survival (DSS), shorter disease-free survival (DFS), less 10-year DSS, less 10-year DFS, and more recurrence. The 5-year DSS and 5-year DFS in the dMMR group only showed a trend of worse survival but did not reach statistical significance. In conclusion, dMMR is present in a significant number of endometrioid endometrial cancers patients and is associated with poorer clinicopathological factors and survival parameters in the long run. dMMR should be considered in the risk stratification of endometrial cancer to guide adjuvant therapy and individualisation for longer follow up plan.

Epigenetic Drifts during Long-Term Intestinal Organoid Culture.

Organoids retain the morphological and molecular patterns of their tissue of origin, are self-organizing, relatively simple to handle and accessible to genetic engineering. Thus, they represent an optimal tool for studying the mechanisms of tissue maintenance and aging. Long-term expansion under standard growth conditions, however, is accompanied by changes in the growth pattern and kinetics. As a potential explanation of these alterations, epigenetic drifts in organoid culture have been suggested. Here, we studied histone tri-methylation at lysine 4 (H3K4me3) and 27 (H3K27me3) and transcriptome profiles of intestinal organoids derived from mismatch repair (MMR)-deficient and control mice and cultured for 3 and 20 weeks and compared them with data on their tissue of origin. We found that, besides the expected changes in short-term culture, the organoids showed profound changes in their epigenomes also during the long-term culture. The most prominent were epigenetic gene activation by H3K4me3 recruitment to previously unmodified genes and by H3K27me3 loss from originally bivalent genes. We showed that a long-term culture is linked to broad transcriptional changes that indicate an ongoing maturation and metabolic adaptation process. This process was disturbed in MMR-deficient mice, resulting in endoplasmic reticulum (ER) stress and Wnt activation. Our results can be explained in terms of a mathematical model assuming that epigenetic changes during a long-term culture involve DNA demethylation that ceases if the metabolic adaptation is disturbed.