NGS in Gallbladder Cancer and Response to Treatment

Overview

Evidence suggests distinct models of molecular and pathologic progression, and a growing body of genetics data points to a heterogeneous collection of underlying mutations in key oncogenes and tumor suppressor genes. Although tumor genetics have been used to tailor individual treatment regimens and guide clinical decision making in other cancers, these principles have not been applied in gallbladder malignancy. Recent clinical trials with targeted therapies seem promising, although the relationships between subsets of patients with positive responses to therapy and tumor genetics remain unexplored.

Gallbladder carcinoma (GBC) is the most common type of biliary tract carcinoma and the third commonest digestive tract malignancy in India. GBC arises in the setting of chronic inflammation and the commonest source is cholesterol gallstones (in more than 75% patients). Other causes of chronic inflammation include primary sclerosing cholangitis, ulcerative colitis, liver flukes, chronic Salmonella typhi and paratyphi infections, and Helicobacter infection. Many other factors have also been identified such as ingestion of certain chemicals, exposures through water pollution, heavy metals and radiation exposure. Only a small fraction of GBC are associated with hereditary syndromes like Gardner syndrome, neurofibromatosis type I and hereditary non-polyposis colon cancer. Of the multiple molecular alterations observed in GBC, it has not yet been possible to pinpoint which ones are the "driver" genes or controllers of the neoplastic process and to differentiate them from the "passenger" genes, those observed mainly in sporadic malignant tumors like GBC in which epigenetic alterations predominate. The most frequently mutated genes in GBC are: TP53 (41%), CDKN2A (28%) KRAS (19%), TERT (8%), CTNNB1 (8%) and PI3K (7%). The signalling pathway of the ERBB family is one of the most frequently mutated in GBC. These receptors participate in regulating cell proliferation, differentiation and survival. Their amplification mainly translates into protein over expression. The receptor HER2/NEU, after dimerization activates a large variety of downstream pathways such as RAS-RAF-MEK-ERK1/2 or PI3k-AKT-MTOR with great influence on cell proliferation. On the other hand, PTEN (phosphatase and tensin homolog) is a tumor suppressor gene that encodes a protein with phosphatase function that inactivates substrates like PI3K The absence of the PTEN functional protein permits the activation of PI3k with an even greater intensity than the activating mutation of PI3K itself. The uncontrolled production of PIP3 is one of the most important effectors of the PI3K/AKT pathway with mTOR stimulating protein synthesis that regulate apoptosis. The immunohistochemical expression of the PTEN protein is considered a good way to evaluate the functional state of the gene. 1. Comprehensive history and physical examination of the patients and all the details will be recorded in the preset proforma. All routine investigations as indicated including a biopsy to establish a diagnosis and CT/MRI/MRCP of the abdomen to measure the tumor dimensions and stage the disease before initiation of treatment will be recorded. 2. The archival tissue will be studied for expression of gene mutation by molecular analysis using Next Generation Sequencing. Patients treated between 2017-2020 where NGS information is available will also be included in retrospect. Their data will be extracted from the Medical records, and attempts will be made to contact them for follow-up.