Cytogenetics of Solid Tumors

Cytogenetics of Solid Tumors - Introduction

• Most neoplasms have genetic abnormalities
• Clonal chromosome aberrations in both benign and malignant neoplasms define particular tumors
• These aberrations refine histopathologic diagnosis, provide prognostic information, and inform therapeutic decisions
• An atypical teratoid/rhabdoid tumor is distinguished from a medulloblastoma
• MYCN gene amplification is documented in a neuroblastoma

Targeted Therapeutic Drugs

• Therapeutic drugs are designed to target a specific genetic anomaly
• Examples:
  • Imatinib mesylate for patients with t(9;22) or BCR-ABL1 fusion
  • ATRA (all-trans retinoic acid) for patients with t(15;17) or PML-RARA fusion
  • Trastuzumab for ERBB2 amplified intraductal breast carcinoma
  • Tyrosine kinase inhibitors for gastrointestinal stromal tumors
• Information to determine optimal therapies is provided by chromosome aberrations for tumors without a known targetable genetic anomaly
• Oligodendroglial brain tumors with der(1;19) or 1p/19q deletion and Wilms tumors with 1p/16q deletion are examples
• Success in oncology has occurred by discovering effective, less toxic regimens for improved life quality and survival
• Increased survival, length of survival and increased cure rate are results of correlation between genetic anomalies of tumors and response to therapy
• Discovery has increased more swiftly for hematologic tumors due to culture ease and genetic information yield via chromosome analysis
• Acquiring knowledge in solid tumors is vital to finding effective therapies.
• Anomalies that influence patient therapy are still being discovered through conventional chromosome analysis
• Chromosome data and newer technologies contribute to growing genetic databases
• These databases are used to design new therapeutic trials and discover new drugs through understanding the genes involved

Solid Tumor Culture and Analysis

• Cytogenetic analysis of solid tumors (STs) is challenging
• STs require more time and effort compared to typical tissues like conception products and skin
• Understanding the "diagnosis" is fundamental to successful outcomes because solid tumors are diverse with many different names
• The diagnosis directs the processing of the sample, preparation, culture type, growth medium times and harvest methods
• Culture must be closely monitored for growth and patterns
• Harvest should happen as soon as mitotic cells are present
• Goal is to capture the malignant cell population and avoid cell confluence and growth of normal cells
• Harvest time and method differ for cell types
• Perseverance and experience are factors in analysis to discern what anomalies have significance for diagnosis and/or therapeutic management

Factors Affecting Solid Tumor Growth

• Tissue culture simulates in vivo environment to support viability/growth
• Knowledge of tumor type influences how it is processed
• Physician or pathologist can provide the tumor type or working diagnosis
• Critical for success of culture is also the condition of the sample
• Surgeon/pathologist obtains sample, imperative they know how to handle for cytogenetic culture
• Working relationship with pathologist(s) can be beneficial
• Critical aspects of tumor sample collection:
  • Sterility must be maintained, non-sterile tumors minimized for contamination. Communication is vital

The Sample Needed

• Needs tumor without surrounding normal tissue.
• Must be viable, not necrotic, frozen, or fixed
• Need delivery ASAP
• Should be stored in supplemented culture medium at room temperature or 37°C, until delivered
• Optimal sample size: 1 cm³ piece of tumor, even small pieces can be cultured successfully
• Touch preparations of tumor provide a good sample for FISH and rapid results.

Tissue culture factors

• Type of culture: suspension or monolayer, monolayer for tumors that need attachment and/or cell-to-cell contact for growth, small round cell tumors grow in suspension
• Type of medium: monolayer cultures do fine using basic supplemented medium, suspension cultures work using supplemented like bone marrow cultures
• Monolayer on coverslips facilitates growth of tiny samples, avoids trypsinization for splitting/harvesting, avoids slides for banding, requires less medium, and allows growth/mitotic activity to be monitored
• Tumor disaggregation usually promotes faster growth
• Culturing with and without enzymatic disaggregation can be initiated with sufficient sample
• Culture initiation is needed ASAP to preserve viability
• Many cultures increases opportunity for feed and harvest for different times to promote growth and capture metaphase cells
• Initiation with a small medium amount allows cells to attach faster, be patient and wait, before flooding
• Observation is needed daily to detect harvest and prevent growth
• May capture metaphase cells with different exposure of Colcemid exposure
• Labs must provide time to culture/analyze samples, critical to management
• Pathologists and oncologists use information to refine and therapeutic decisions
• Chapter covers solid tumors with known abnormalities documenting pathological and clinical significance for diagnosis, diagnostic subtype, prognosis, and therapeutic intervention

Central Nervous System Tumors (CNS)

• Gliomas: common primary tumors, include astrocytomas oligodendrogliomas, and ependymomas.
• Features for classification and grading correlate with prognosis and guide therapy
• Annual incidence of primary brain tumors is ~8–12 in 100,000, intraspinal tumors 1-2 in 100,000.
• CNS tumors are the most common (~20%) cancers

Chromosome Abnormalities with Diagnostic or Clinical Significance in Tumors of The Central Nervous System