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F ew words strike fear quite like “cancer,” but what
exactly is it, and how might it impact decisions
about medical fitness to dive?
Cancer is a broadly applied term used
to describe cells that exhibit abnormal and
unregulated replication, growth and activity.
These aberrant cellular behaviors can arise from alterations
in DNA, or they may stem from environmental factors that
disrupt DNA and thus impact normal cellular functioning.
When this occurs, cells can lose the ability to control growth
and may even become resistant to normal programmed cell
death. Tissue masses that form as a result of this unchecked
proliferation are commonly known as tumors or neoplasms,
which means “new growths.” If there is a genetic basis for
a neoplasm, the altered DNA can be passed to daughter
cells, which then proliferate and spread. Cancer’s capacity
to impact health stems from these alterations in cellular
activity, which interrupt or disrupt normal organ function
sufficiently to cause illness.
Cancer is the second-leading cause of death in the United
States. The American Cancer Society predicts that in 2013
an estimated 1.6 million people will be diagnosed.1 With
statistics like this, it is likely that you or someone you know
has been or will be affected.
Benign or Malignant
Neoplasms are described as either benign or malignant
— designations that are based on their potential behavior.
Benign tumors generally remain localized to their site of
origin, and most develop a fibrous capsule that separates
them from surrounding tissue, which can make them
amenable to surgical removal. While such tumors usually
don’t spread from their site of origin, their size and location
nonetheless can lead to significant disease if they are present
in vital areas such as the brain. In this way, benign tumors
that grow in confined spaces or impact other structures may
be every bit as lethal as their malignant counterparts.
Malignant tumors are those most commonly referred to
as cancers. Malignancy implies that the tumor can invade
and destroy adjacent structures and metastasize (spread
to distant sites). While not all malignant tumors behave the
same, all warrant concern. The infiltrative nature of these
tumors generally prompts aggressive treatment, which
may include a combination of chemotherapy, radiation
and surgery.
Diagnosis
Early detection offers the greatest hope for successful
treatment. Screening has been shown to improve survival in
several types of cancers. Recommended health-maintenance
examinations include mammograms, cervical cytology
(previously known as Papanicolaou or “Pap” smears) and
colonoscopies. To demonstrate the thought process and
methodology of one of these screening approaches, let’s take
a closer look at colon cancer, which is the second-leading
cause of cancer deaths in the United States (after lung
cancer).
The U.S. Preventive Services Task Force recommends
screening for colon cancer beginning at age 50 and
continuing every 10 years until about age 75 for people of
average risk.2 Colonoscopy enables detection of colon cancer
as well as discovery and removal of early precancerous
growths. Commonly beginning as small, benign lumps
known as adenomatous polyps, these tumors may be visible
in the lumen of the colon. Colonoscopy enables direct
visualization of the colon’s inner surface via a camera lens
connected to a flexible tube. If a polyp or other abnormal
growth is detected, a tissue sample (biopsy) can be taken
for further evaluation. A microscopic evaluation by a
pathologist is necessary to confirm whether the biopsy is
normal or neoplastic.
Typically, the first things a patient wants to know after
being diagnosed with cancer is: Has it spread, and what
is the prognosis (expected outcome)? To help provide a
framework for such discussions and to guide treatment, early
medical and surgical efforts are geared toward determining
the grade and stage. A tumor’s grade is a measure of its
cellular abnormality or degree of differentiation from its
tissue of origin. Staging is based on the size of the primary
tumor, the extent of local invasion, the spread to local lymph
nodes and the presence of tumors in other areas of the body.
Grade and stage are determined using techniques including
clinical findings, microscopic evaluation of biopsied tissue,
cytology, computerized tomography (CT), positron emission
tomography (PET), magnetic resonance imaging (MRI) and
surgical exploration.
Treatment
Current treatment modalities fall into four basic categories:
surgery, chemotherapy, radiation and bone marrow
transplantation. The specific therapeutic approach to a given
cancer is influenced by many factors including size, grade
and stage, location, tumor genetics (which may indicate
the tumor type and sensitivity to treatment), likelihood
of treatment success, risk of treatment and probability
of recurrence. Treatment modalities are often provided
together or in sequence to achieve remission, reduce a
tumor’s impact on health or simplify surgical removal.
Surgery
Surgical removal of abnormal tissue is often the first-line
treatment, and it can enable both gross and microscopic
evaluation of tissue. Excision of wide margins of normal-
appearing tissue along with areas of visible disease is
frequently performed in an attempt to increase the likelihood
of complete removal of the cancer cells and to minimize