Primary mucinous adenocarcinoma of the vermiform appendix with high grade microsatellite instability

Landscape of Genetic Mutations in Appendiceal Cancers

In appendiceal cancers, the most frequently mutated genes are (i) KRAS, which, when reactivated, restores signal transduction via the RAS-RAF-MEK-ERK signaling pathway and stimulates cell proliferation in the early stages of tumor transformation, and then angiogenesis; (ii) TP53, whose inactivation leads to the inhibition of programmed cell death; (iii) GNAS, which, when reactivated, links the cAMP pathway to the RAS-RAF-MEK-ERK signaling pathway, stimulating cell proliferation and angiogenesis; (iv) SMAD4, exhibiting typical tumor-suppressive activity, blocking the transmission of oncogenic TGFB signals via the SMAD2/SMAD3 heterodimer; and (v) BRAF, which is part of the RAS-RAF-MEK-ERK signaling pathway. Diverse mutations are reported in other genes, which are part of secondary or less critical signaling pathways for tumor progression, but which amplify the phenotypic diversity of appendiceal cancers. In this review, we will present the main genetic mutations involved in appendix tumors and their roles in cell proliferation and survival, and in tumor invasiveness, angiogenesis, and acquired resistance to anti-growth signals.

Inherited Cancer Susceptibility Gene Sequence Variations Among Patients With Appendix Cancer

Importance

Germline sequence variations in APC, BMPR1A, CDH1, CHEK2, EPCAM, MLH1, MSH2, MSH6, MUTYH, PMS2, PTEN, SMAD4, STK11, and TP53 genes are associated with susceptibility to gastrointestinal cancers. As a rare cancer, the evaluation of appendiceal cancer (AC) predisposition has been limited.

Objective

To assess the prevalence and spectrum of inherited cancer susceptibility gene sequence variations in patients with AC and the utility of germline genetic testing for this population.

Design, Setting, and Participants

This cohort study included patients with AC who underwent germline genetic testing of 14 cancer susceptibility genes performed by a clinical testing laboratory between March 1, 2012, and December 31, 2016. Data were analyzed from March to August 2022. Clinical, individual, and family histories were obtained from clinician-completed test requisition forms. Multigene panel testing was performed by targeted custom capture and sequencing and chromosome rearrangement analysis.

Main Outcomes and Measures

The main outcomes were germline sequence variation prevalence and spectrum in patients with AC.

Results

Among the 131 patients with AC in the cohort (90 female [68.7%]), a total of 16 deleterious sequence variations were identified in 15 patients (11.5%). Similarly, when limited to the 74 patients with AC as the first and only primary tumor, a total of 8 patients (10.8%) had at least 1 deleterious sequence variation in a cancer susceptibility gene. Overall, 6 patients (4.6%) had a deleterious sequence variation observed in MUTYH (5 with monoallelic MUTYH and 1 with biallelic MUTYH). All 4 patients with Lynch syndrome (3.1%) had a sequence variation in the MLH1 gene, of whom 3 were aged 50 years or older at AC diagnosis. Five patients (3.8%) had deleterious sequence variations in other cancer predisposition genes (1 with APC [c.3920T>A, p.I1307K], 2 with CHEK2 [c.470T>C, p.I157T], 1 with SMAD4 [c.263 287dup, p.L98IFS*14], and 1 with TP53 [c.524G>A, p.R175H]).

Conclusions and Relevance

In this cohort study, 1 in every 10 patients with AC who underwent testing for hereditary cancer predisposition carried an inherited gene sequence variation associated with cancer susceptibility. Given the high frequency and broad spectrum of germline gene sequence variations, these data suggest that genetic evaluation might be warranted for all patients diagnosed with this rare malignant tumor. A systemic sequencing effort for all patients with AC may also identify cancer vulnerabilities to exploit for therapeutic development in a cancer type for which clinical trials are limited.

Molecular and Genetic Markers in Appendiceal Mucinous Tumors: A Systematic Review

INTRODUCTION

The role of somatic mutation profiling in the management of appendiceal mucinous tumors (AMTs) is evolving. Using a systematic review, we identified somatic alterations (SAs) that comprise histopathologic types of AMTs and those associated with aggressive clinical phenotypes.

METHODS

MEDLINE/PubMed was searched for studies on AMTs including molecular markers or genomic alterations, published between 1990 and 2018. Studies were grouped under low- and high-grade histological type for primary and metastatic tumors.

RESULTS

Twenty-one studies involving 1099 tumors (primary/metastatic) were identified. Seven studies involving 101 primary low-grade AMTs identified KRAS (76.5%) as the predominant SA. Four studies noted GNAS in 45.2% of 42 low-grade appendiceal mucinous neoplasms, and KRAS was identified in 74.4% of 14 studies with 238 low-grade pseudomyxoma peritonei (PMP). GNAS was noted in 56% of 101 tumors and TP53 was noted in only 9.7% of 31 tumors. Primary high-grade tumors demonstrated lower SAs in KRAS (50.4% of 369 tumors) and GNAS (27.8% of 97 tumors), and higher SAs in TP53 (26.0% of 123 tumors). In high-grade PMP, SAs were noted in KRAS (55.0% of 200 tumors), GNAS (35.0% of 60 tumors), and TP53 (26.3% of 19 tumors). No clear association was noted between SAs and survival.

CONCLUSIONS

KRAS and GNAS are frequently altered in low-grade AMTs, while TP53 is frequently altered in high-grade AMTs, with no apparent change in expression between primary and metastatic tumors. Although SAs may provide valuable insights into variability in tumor biology, larger studies utilizing clinically annotated genomic databases from multi-institutional consortiums are needed to improve their identification and clinical applicability.

Adenocarcinoma of the Appendix Presenting as a Palpable Right Thigh Mass

Intra-abdominal and intra-pelvic pathologies initially presenting in extra-abdominal/pelvic locations is unusual. This spread predominantly occurs with infectious processes to sites including the buttock, thigh, and calf. The routes of extension into adjacent anatomically weak compartments include the pelvic outlet, greater sciatic foramen, obturator foramen, inguinal or femoral canal, weak bones, or along nerves and blood vessels. Malignant neoplasms of the appendix, while extremely rare and accounting for only 0.4% of all gastrointestinal cancers, is one of the intra-abdominal pathologies that can spread via these routes. Adenocarcinoma of the appendix accounts for 10-20% of primary appendiceal tumors. They usually present as acute appendicitis or as a right lower quadrant abdominal mass when associated with a mucocele. We report the unique case of mucinous appendiceal adenocarcinoma in a 57-year-old male who initially presented with a right thigh mass secondary to extension of the neoplasm from the right lower quadrant through the femoral canal. A similar presentation of a mucinous appendiceal cystadenoma has been previously reported, however, to our knowledge, this is the first case of a malignant appendiceal tumor extending into the thigh. We review the literature and discuss imaging findings and treatment of this tumor.

Adenocarcinoma mimicking appendicular lump: a diagnostic dilemma-a case report

Background

Primary appendiceal adenocarcinoma is a rare tumor, mucinous variety being common. This case is reported to highlight the unusual presentation and diagnostic difficulty of appendiceal adenocarcinoma.

Case presentation

Patient presented with acute appendicitis with ill-defined tender lump which responded to conservative management.

Conclusions

High index of suspicion should be kept in mind for elderly patients presenting with appendicular lump. Every effort should be made during elective appendectomy to remove stump in case of sloughed out appendix.

DNA damage response and its clinicopathological relationship in appendiceal tumors

BACKGROUND

Appendiceal tumors are rare, and their pathogenesis is not well known. DNA damage response (DDR) is a sequence from the detection of damaged DNA to the repair, and its impairment is implicated in the progression of cancers. The aim of the current study is to explore the expression and phosphorylation of checkpoint kinase 2 (Chk2) and TP53, which are key molecules in DDR, and their clinicopathological correlation in the appendiceal tumors.

METHODS

Chk2, phosphorylated Chk2 (pChk2), and TP53 were immunostained in 4 cases of adenoma (AD), 5 non-mucinous adenocarcinomas (AC), 29 low-grade appendiceal mucinous neoplasms (LAMN), and 7 mucinous adenocarcinomas (MAC). Ki-67 labeling index was also evaluated by immunostaining.

RESULTS

Chk2 was highly expressed in the nuclei of all the appendiceal tumors. While pChk2 was high in AD, LAMN, and MAC, it was reduced in AC. Nuclear positive reaction of TP53 was lower in LAMN compared with those of other tumors. The Ki-67 labeling index was slightly lower in LAMN than those in other tumors. The recurrence and death in LAMN is infrequent compared with those in AC and MAC.

CONCLUSIONS

The current study suggested the impairment of DDR in AC and MAC. DDR appeared to be preserved in LAMN, and it may account for low proliferating activity and a favorable clinical course in LAMN.

High-level microsatellite instability in appendiceal carcinomas

High-level microsatellite instability (MSI-high) is found in approximately 15% of all colorectal adenocarcinomas (CRCs) and in at least 20% of right-sided cancers. It is most commonly due to somatic hypermethylation of the MLH1 gene promoter region, with familial cases (Lynch syndrome) representing only 2% to 3% of CRCs overall. In contrast to CRC, MSI-high in appendiceal adenocarcinomas is rare. Only 4 MSI-high appendiceal carcinomas and 1 MSI-high appendiceal serrated adenoma have been previously reported, and the prevalence of MSI in the appendix is unknown. We identified 108 appendiceal carcinomas from MD Anderson Cancer Center in which MSI status had been assessed by immunohistochemistry for the DNA mismatch-repair proteins MLH1, MSH2, MSH6, and PMS2 (n=83), polymerase chain reaction (n=7), or both (n=18). Three cases (2.8%) were MSI-high, and 1 was MSI-low. The 3 MSI-high cases included: (1) a poorly differentiated nonmucinous adenocarcinoma with loss of MLH1/PMS2 expression, lack of MLH1 promoter methylation, and lack of BRAF gene mutation, but no detected germline mutation in MLH1 from a 39-year-old man; (2) an undifferentiated carcinoma with loss of MSH2/MSH6, but no detected germline mutation in MSH2 or TACSTD1, from a 59-year-old woman; and (3) a moderately differentiated mucinous adenocarcinoma arising in a villous adenoma with loss of MSH2/MSH6 expression, in a 38-year-old man with a strong family history of CRC who declined germline testing. When the overall group of appendiceal carcinomas was classified according to histologic features and precursor lesions, the frequencies of MSI-high were: 3 of 108 (2.8%) invasive carcinomas, 3 of 96 (3.1%) invasive carcinomas that did not arise from a background of goblet cell carcinoid tumors, and 0 of 12 (0%) signet ring and mucinous carcinomas arising in goblet cell carcinoid tumors. These findings, in conjunction with the previously reported MSI-high appendiceal carcinomas, highlight the low prevalence of MSI in the appendix as compared with the right colon and suggest that MLH1 promoter methylation is not a mechanism for MSI in this location.

Unusual histopathological findings in appendectomy specimens from patients with suspected acute appendicitis

AIM: To investigate the prevalence and implications of unusual histopathological findings in appendectomy specimens from patients with suspected acute appendicitis.

METHODS: The demographic and histopathological data of 1621 patients (≥ 16 years-old) who underwent appendectomy to treat an initial diagnosis of acute appendicitis between January 1999 and November 2011 were retrospectively assessed. Microscopic findings were used to classify the patients under six categories: appendix vermiformis, phlegmonous appendicitis, gangrenous appendicitis, perforated appendicitis, supurative appendicitis, and unusual histopathologic findings. The demographic and clinicopathologic characteristics of patients with unusual histopathologic findings were evaluated in detail, and re-analysis of archived resected appendix specimens was carried out.

RESULTS: A total of 912 males and 709 females, from 16 to 94 years old, were included in the study and comprised 789 cases of suppurative appendicitis, 370 cases of appendix vermiformis, 243 cases of perforated gangrenous appendicitis, 53 cases of flegmaneous appendicitis, 32 cases of gangrenous appendicitis, and 134 (8.3%) cases of unusual histopathological findings. The unusual histopathological findings included fibrous obliteration (n = 62), enterobius vermicularis (n = 31), eosinophilic infiltration (n = 10), mucinous cystadenoma (n = 8), carcinoid tumor (n = 6), granulomatous inflammation (n = 5), adenocarcinoma (n = 4; one of them mucinous), and mucocele (n = 3), adenomatous polyp (n = 1), taenia sup (n = 1), ascaris lumbricoides (n = 1), appendiceal diverticula (n = 1), and B cell non-hodgkin lymphoma (n = 1). None of the 11 patients with subsequent diagnosis of tumor were suspected of cancer prior to the appendectomy.

CONCLUSION: Even when the macroscopic appearance of appendectomy specimens is normal, histopathological assessment will allow early diagnosis of many unusual diseases.