Medical experts talk about popular science | A brief discussion on "Molecular Pathology and Precision Diagnosis"

"Pathology is the foundation of medicine", "pathologists are doctors' doctors", and pathological diagnosis is the "gold standard" for the diagnosis of diseases, especially tumor diseases. These are the long-standing evaluations of pathology in the medical community. It is with such a "halo" that every pathologist is walking on thin ice every day. The only way is to keep learning, overcome difficulties and meet challenges, and do their best to meet the clinical expectations and requirements for pathology. New era, new challenges. With the rapid development of the times and the great progress of science and technology, traditional pathology has entered the era of molecular pathology. As molecular pathology diagnosis is widely used in clinical practice, clinical medicine has entered the era of precision medicine.

Molecular pathology is formed by the integration and penetration of molecular biology, genetics, immunology and other disciplines on the basis of traditional pathological morphology. It explores the molecular genetic changes of cells and tissues at the genetic level, reveals the laws of disease occurrence and development, and clarifies the nature of the disease. Molecular pathological diagnosis is based on morphology and uses modern molecular biological techniques to detect biological macromolecules such as DNA, RNA, and proteins in pathological specimens such as tissues or cells to achieve accurate diagnosis of the disease. Molecular pathological diagnosis is the premise and guarantee of precision medicine.

Molecular pathology diagnosis is also called molecular pathology examination or molecular pathology testing. Molecular pathology testing focuses on the "internal root" of the disease and plays an important role in clarifying the diagnosis, guiding individualized treatment, predicting treatment response and determining prognosis. Common molecular pathology testing techniques include chromogenic in situ hybridization, fluorescent in situ hybridization (FISH), polymerase chain reaction (PCR) and next-generation sequencing (NGS). The following is a brief introduction to the application of molecular pathology testing in three aspects: (1) determining the pathological diagnosis and typing of tumors; (2) molecular target detection and companion diagnosis; and (3) genetic risk assessment.

| Determine the pathological diagnosis and classification of the tumor

Tumors with different molecular genetic characteristics have different biological behaviors, treatments and prognoses. At present, the pathological diagnosis of tumors has shifted from morphological classification to molecular classification. Genetic testing helps to accurately diagnose tumors that are difficult to diagnose based on morphology. For example, EBV and HPV in situ hybridization testing for cervical lymph node metastatic squamous cell carcinoma with unknown primary lesions can not only determine the etiology subtype classification of the tumor, but also infer the primary site of the tumor and judge the treatment response and prognosis. If EBV is positive, it may come from the nasopharynx. If HPV is positive, it indicates HPV infection-related squamous cell carcinoma from the oropharynx, tonsils and other parts, and the prognosis of this tumor is good. For another example, in the diagnosis of tumors that appear as spindle cells morphologically, if the molecular test has C-KIT gene mutation, it is very likely to be a gastrointestinal stromal tumor. The presence of JAZF1-SUZ12 gene fusion may be a low-grade endometrial stromal sarcoma. The discovery of SS18-SSX1/2/4 gene fusion can be determined as a synovial sarcoma. If the molecular test results show MDM2 gene amplification, it is most likely a dedifferentiated liposarcoma. In recent years, new diseases based on genetic changes have continued to emerge. For example, t(6;11) renal cancer, Xp11.2 translocation/TFE3 gene fusion-related renal cancer, and succinate dehydrogenase (SDH)-deficient renal cancer have been newly added to renal tumors. These are named according to the corresponding molecular genetic changes. Molecular pathology testing is of great significance in the diagnosis of such tumors. In addition, there are tumors named according to molecular genetic changes in soft tissue, central nervous system, lymphohematopoietic, respiratory and other multi-organ system tumors. Without molecular testing, a clear diagnosis cannot be made, and subsequent clinical treatment is out of the question.

| Molecular target detection and companion diagnostics

Molecular target detection is the premise for guiding individualized treatment, and is also called the companion diagnosis of tumor treatment. Targeted therapy is to design corresponding therapeutic drugs at the molecular level for the already clear carcinogenic etiology. When the drug enters the body, it will act specifically on the carcinogenic site, causing tumor cells to die specifically without affecting normal cells. Therefore, molecular targeted therapy is also called "biological missile". If the patient has a corresponding therapeutic target gene mutation, the targeted drug will take effect quickly and has a high efficiency. It can quickly relieve the symptoms caused by the tumor, improve the patient's quality of life, and significantly improve the survival rate. At present, many solid tumors have abnormal gene targets and molecular targeted drugs. Molecular target detection should be performed before targeted therapy, such as detecting EGFR, ALK, ROS1 and other gene mutations in lung cancer patients; detecting HER2 gene amplification in breast cancer; detecting BRAC gene mutations in ovarian cancer; detecting KRAS, NRAS, BRAF genes, mismatch repair genes in colorectal cancer; detecting C-KIT and PFGFRA genes in gastrointestinal stromal tumors, etc. The "Guidelines for the Clinical Application of New Anti-tumor Drugs (2020 Edition)" issued by the National Health Commission clearly states that the clinical application of anti-tumor drugs must be confirmed by pathological histology or genetic testing. Molecular pathology testing covers a variety of testing technologies. Pathologists will choose the most reasonable testing methods and testing items according to the type and condition of the patient's disease to escort the patient's individualized diagnosis and treatment.

| Genetic and disease recurrence risk assessment

Molecular testing can also be used to assess and predict disease risks. In 2013, Angelina Jolie, a famous American movie star, discovered through gene sequencing that she carried a BRCA1 (breast cancer susceptibility gene, BRCA) gene mutation. Due to her family history of cancer, she decided to undergo a preventive mastectomy. Two years later, she underwent surgery again to remove her ovaries and fallopian tubes, which attracted global attention to the BRCA test for hereditary breast and ovarian cancer susceptibility genes. BRCA is a tumor susceptibility gene. Tumor susceptibility gene testing mainly assesses the genetic risk of the subject to develop cancer in the future, helping us to detect health "mines" early - disease susceptibility genes, and take positive and effective methods to proactively and targetedly intervene in advance to prevent the occurrence of tumors. Once harmful mutations in hereditary tumor susceptibility genes are found, immediate family members can also be reminded to undergo germline testing to assess the risk of tumors. Another example is Lynch syndrome, also known as hereditary non-polyposis colon cancer. It is an autosomal dominant genetic disease with molecular characteristics of high microsatellite instability (MSI-H) or germline pathogenic mutations in mismatch repair (MMR)-related genes (including MLH1, MSH2, MSH6, PMS2, and EPCAM, etc.). It can cause a variety of tumor syndromes, with colorectal cancer and endometrial cancer being the most common manifestations. Lynch syndrome accounts for 5%-15% of all colorectal cancers. In addition to colorectal cancer and endometrial cancer, cancers can also occur in the ovaries, stomach, small intestine, liver and gallbladder, kidneys, ureters, brain, and skin. The NCCN guidelines clearly state that all patients with colorectal cancer and all patients with endometrial cancer should undergo MMR or MSI testing and genetic risk assessment to detect Lynch syndrome patients early.

In summary, extensive molecular pathology examinations for molecular pathology diagnosis of diseases is currently the primary task of the pathology department, an inevitable requirement for precision medicine, and an important indicator of the overall medical quality and level of the hospital.

Author: Gao Hongwen

Doctor of Medicine, Professor, Chief Physician, Doctoral Supervisor, and Director of the Department of Pathology, Jilin University Second Hospital.

He is currently a standing member of the Pathology Branch of the Chinese Medical Association, a standing member of the Pathology Branch of the Chinese Medical Association, the head of the head and neck disease group of the Pathology Branch of the Chinese Medical Association, the chairman of the Pathology Branch of the Jilin Provincial Medical Association, the chairman of the Pathology Committee of the Changchun Medical Association, the member of the Pathology Group of the Obstetrics and Gynecology Branch of the Chinese Medical Association, and the editorial board member of the Chinese Journal of Pathology. He has won honorary titles such as "National Advanced Worker in the Health System" and "Young and Middle-aged Professional and Technical Talents with Outstanding Contributions in the Health System of Jilin Province". He is good at tumor pathology diagnosis.

| Discipline Introduction

The Department of Pathology of the Second Hospital of Jilin University was founded in 1961. It is one of the first national key clinical specialty construction units, a key laboratory unit for molecular pathology diagnosis of tumors in Jilin Province, a key medical specialty in Changchun City, and a dominant discipline of the Second Hospital of Jilin University. There are 42 staff members, 7 senior doctors, and 2 doctoral supervisors. The sub-specialties of pathology such as female reproductive system, head and neck, chest, breast, male reproductive and urinary system, molecular pathology and scientific research have been initially established. The annual pathological tissue biopsy volume is more than 60,000 cases, and the annual external difficult pathology consultation is more than 3,000 cases. It has established a good cooperative relationship with the pathology departments of affiliated hospitals such as Tohoku University, Okayama University, and Seoul National University in South Korea.