Molecular Diagnosis in Pathology: The Bridge to the 21st Century
Moderators: Dr. Ricardo Lloyd and Dr. George Kontogeorgos
Section 7 -
Molecular Diagnosis of Head and Neck Tumors
Adel El-Naggar MD, PhD
UT MD Anderson Cancer Center
Head and neck neoplasms encompass a spectrum of widely varied histogenetic and morphologic
entities. The most commonly encountered pathologies are those of mucosal surfaces followed by thyroid
and salivary gland origin. Although relatively uncommon and less lethal than major human cancers, these
tumors may pose diagnostic difficulties and cause considerable functional and physical morbidities to
their subjects. These inherent characteristics along with the anatomic complexities and the variable
biological behavior mandated a central role for their multidisciplinary clinical assessment.
Head and Neck pathology:
The traditional practice of head and neck pathology began in the 1950s and 1960s and
continued to be the primary means of diagnosis and pathological evaluation of head and neck specimens.
The last four decades have also witnessed major improvements and additions to the diagnosis and
classification of pre-malignant squamous lesions, squamous carcinoma subtypes, and thyroid and salivary
tumors. However, the heterogeneous and unpredictable clinical behavior of these tumors within defined
stages and the increasing practice of multimodality therapy demand additional biological end-points to
supplant the clinicopathologic stratification of patients. It was found that alterations in cancer
cell genotype are manifested in specific changes of cell physiology, morphology and organization of tumor
cells which are fundamental to morphologic diagnosis. These modifications are operative in most human
tumor types. However, the paths that cells take in becoming malignant varies widely and reflect on the
nature, extent, and timing of the molecular events within and between tumors. As a consequence, the
acquisition of biological capabilities of cancer cells may appear at various times during a given tumor
progression and independent of the order of genetic pathways involved.
Cancer is a biologically complex disease that is primarily influenced by interactions
between extra cellular forces and incipient cancer cells resulting in physiologic and phenotypic changes
that collectively dictate the malignant growth. This led to the conceptual formation of tumorigenesis as
a multistep process of alteration in the genome leading to the progressive transformation of normal human
cells into highly malignant derivatives. Changes coincidental to the malignant phenotype include
independent growth signaling, insensitivity to inhibitory factors, sustained cell-survival, unlimited
proliferative potential, enhanced angiogenesis and tissue invasion and metastasis. These defined
characteristics are complementary to each other and are shared with variable degrees and emphasis among
human neoplasias. Critical factors in these pathways that reflect derangements in the physiologic
characteristics are ideal markers in head and neck and other tumors.
The unraveling of the DNA double helical structure in the 1950s and the discovery of the
dominant oncogenes and the recessive tumor genes in the 1960s and 1970s have led to a new era of
molecular investigations. Then, as followed in the mid 1980s, the recognition of the epigenetic
modification was found to play a major role in human pathologies and tumor evaluation. It was
subsequently found that several tumors develop in an age-dependent manner implicating a set of
rate-limiting stochastic events in most sporadic human tumors. Identifying and validating crucial
markers for these vital processes are ideal candidates in tumor assessment.
The convergence of head and neck surgical pathology and molecular genetics commenced in
the early and mid 1990s. Such occurrences opened vast new opportunities for academic pathologists to
revisit the histogenesis and biology of these tumors. It also raised many challenges for the future
practice of diagnostic surgical pathology. The development of protocols for DNA, RNA, and protein
extraction from archival tissue materials in the late 1980s and early 1990s has played a major role in
the success of these efforts. A plethora of retrospective studies using pathologically characterized
tissue has allowed for the partial characterization of the molecular abnormalities of some of these
tumors. Initially, most efforts focused on the squamous tumorigenesis as an ideal model for molecular
progression for accessibility and better visualization and localization of early pre-malignant lesions.
The model also in contrast to thyroid and salivary gland tumors, is characterized by well-defined
pre-malignant progressive morphologic stages. On the other hand, because of the lack of intermediate and
pre-malignant stages of salivary and thyroid neoplasms, studies of these tumors are largely
inconclusive. The limitations of using archival tissues on the extent and reliability of these results
were soon realized. Studies have shown that formalin fixation lead to extracted nucleic acids and
proteins underscoring the necessity for the establishment of frozen tissue banking of head and neck
tumors. In 1991 we began the systematic banking of histologically non-tumorous and tumor frozen tissue
which allowed us to better study these tumors.
Advances in molecular genetic and analytical tools in the last four decades have allowed
for the generation of qualitative and quantitative techniques that identify alteration targets using DNA,
RNA, and protein from tumor and host samples. A variety of materials can be used including tissue
biopsies, fine needle aspiration, and body secretion. Molecular markers of critical cellular pathways
including cell proliferation, apoptosis, differentiation, and cell adhesions are logical targets for
these markers. These biological markers must be objective, reproducible, cost-effective and subject to
quality control assurance guidelines.
The morphologic-based practice remains the time-honored principal in the pathologic
evaluation of mucosal, salivary and thyroid gland neoplasms. Similarly, traditional clinicopathologic
parameters used in assessing the clinical response and behavior of tumors in practice remained unchanged
for the last three decades.
Because of the pivotal pathology responsibilities for handling the gross and histologic
evaluation ofpatients' tissue materials, it is natural that pathologists will play a primary role in
integrating phenotypic and molecular features in a single molecular pathology report. The presentation
will highlight the progress of molecular pathology in head and neck tumors and the crucial role of
pathologists in this field.
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