Abstract 1379
Background
MMR testing is performed to screen Lynch Syndrome, evaluate the prognosis of colorectal cancer (CRC) and predict the efficacy of PD1/PDL1 blockade in all tumor types. Two methods are available: immunohistochemistry (IHC) using antibodies against MMR proteins and molecular biology (MB) for assessing microsatellite instability (MSI). Classically, dMMR tumor corresponds to loss of expression of two proteins (MLH1 and PMS2 or MSH2 and MSH6) associated with MSI. Atypical profiles of dMMR tumors have sporadically been described. The aim of our study was to describe the frequency and characteristics of these atypical cases.
Methods
All MMR testing performed in our center between 2007 and 2017 were checked to select cases with both available IHC and MB. Then, all dMMR cases were reviewed to identify atypical cases which were defined by: isolated loss of expression of one protein, loss of expression of two proteins without MSI, normal expression of the four proteins with MSI, aberrant loss of proteins, or MSI-low. Biological data of atypical cases were controlled and clinical data were collected for each case.
Results
4948 MMR tests were performed, 3800 had both available IHC and MB data, and 585 were dMMR (15 %). Among them, 97 cases were atypical and after biological control, 8 cases were re-classified typical; allowing to finally identify 89 atypical cases: 60 CRC, 10 endometrial carcinoma, 8 digestive non CRC and 11 others types of cancers. A strong correlation with genetic syndromes was observed for those atypical profiles.Table:
2015P
Isolated PMS2 or MSH6 loss n = 53 | Expression of the four proteins n = 5 | MSH2/MSH6 or MLH1/PMS2 loss n = 16 | Aberrant loss of proteins n = 15 | |
---|---|---|---|---|
MSI | 43 | 3 | - | 13 |
MSI low | 1 | 2 | 8 | - |
MSS * | 9 | - | 8 | 2 |
Clinical characteristics | Predominantly CCR Genetic predisposition syndrome (73%) | Exclusively CCR or endometrial Genetic predisposition syndrome (≥40%) | Predominantly Non CRC (63%) | None |
(* MSS: microsatellite stability)
Conclusions
Even using controlled IHC and MB, 15% of dMMR tumors have an atypical profile. These atypical cases mainly involve non CRC cancer with a strong prediction for Lynch syndrome. Their therapeutic impact particularly for immunotherapy should be now evaluated.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.
Resources from the same session
3309 - Heat Shock Protein 90 chaperones and Protein Kinase D3 regulates androgen-independent prostate cancer development
Presenter: Attila Varga
Session: Poster Display session 1
Resources:
Abstract
3441 - The SWI/SNF driven reprograming for the AR cistrome is NSD2 dependent
Presenter: Katia Ruggero
Session: Poster Display session 1
Resources:
Abstract
1659 - IGF1R inhibition affects the survival of HT29 cancer cells by alterations of the TLR9- and autophagy signaling
Presenter: Györgyi Műzes
Session: Poster Display session 1
Resources:
Abstract
1657 - Modulation of TLR9-dependent autophagy response via inhibition of c-Met signaling influences the survival of HT29 cancer cells
Presenter: Ferenc Sipos
Session: Poster Display session 1
Resources:
Abstract
3045 - Positive Feedback Activation of Notch Signal by Obesity Enhances Colorectal Tumorigenicity
Presenter: Dake Chu
Session: Poster Display session 1
Resources:
Abstract
2285 - The Pathological and Functional Roles of BRPF1 in Hepatocellular Carcinoma
Presenter: Lai Hung Carol Cheng
Session: Poster Display session 1
Resources:
Abstract
3210 - Protein tyrosine phosphatase non-receptor type 3 (PTPN3) could be a new therapeutic target for pancreatic cancer.
Presenter: Akio Yamasaki
Session: Poster Display session 1
Resources:
Abstract
3920 - A Novel bispecific BCMAxCD3 T cell engaging antibody that treat multiple myeloma (MM) with minimal cytokine serection
Presenter: Zhenyu Li
Session: Poster Display session 1
Resources:
Abstract
2691 - Quantitative spatial profiling of lymphocyte-activation gene 3 (LAG-3)/major histocompatibility complex class II (MHC II) interaction in gastric and urothelial tumors
Presenter: Cyrus Hedvat
Session: Poster Display session 1
Resources:
Abstract
2182 - Evaluating the prevalence of the expression of PD-L1 in NSCLC specimens with short-duration formalin fixation using IHC 22C3 pharmDx
Presenter: Keiichi Ota
Session: Poster Display session 1
Resources:
Abstract