Despite advances in both the diagnosis and treatment of breast cancer, the disease remains a leading worldwide health concern.
Now, a new imaging technology under investigation at the Biodesign
Institute at Arizona State University may help researchers pinpoint
subtle aberrations in cell nuclear structure, the molecular biosignature
of cancer, thus significantly improving diagnostic accuracy and
prognosis by providing early detection of the disease.
The team, led by Professor Deirdre Meldrum, ASU Senior Scientist and
Director of the Center for Biosignatures Discovery Automation at
Biodesign has examined normal, benign and malignant cells, using the
first and only research Cell-CT (VisionGate, Inc., Phoenix, AZ)—a
specialized instrument capable of imaging cells in vivid 3-D with true
isotropic resolution. The technology permits the examination of subtle
cellular details inaccessible by more conventional forms of microscopy
that are inherently 2-D.
The 3-D movie images of cells observed in the study reveal numerous
telltale traces of their condition as normal or aberrant. Professor
Meldrum says "there are numerous quantitative morphological parameters
that are indicative of disease and may be used as biosignatures for
disease staging and diagnosis. For example, a cancerous cell typically
has an enlarged nucleus, nuclear invaginations, chromosome mutations,
and unique nuclear shape changes."
Breast cancer remains the most common cancer in women. In 2011, an
estimated 232, 000 new cases were diagnosed and some 39,000 fatalities
occurred. Over a normal lifetime, 1 in 8 women will be diagnosed with
the disease. In general, breast cancer begins either in the ducts of the
mammary gland, (ductal carcinomas) or the lobes of the breast (lobal
carcinomas).
Currently, the definitive clinical diagnosis of malignancy relies on
careful examination of the nuclear structure of cells that have been
prepared by histological staining and subjected to bright field
microscopy. According to Vivek Nandakumar, lead author of the current
study, pathologists qualitatively examine cell features including
nuclear size, shape, nucleus-to-cytoplasm ratio, and the texture of cell
chromatin. However, these observations do not involve quantitative
measurements that would promote a more accurate analysis.
Meldrum concurs, as to the shortcomings of traditional pathology. As
director of the Microscale Life Sciences Center, an NIH Center of
Excellence in genomic science, she has devoted much of her career to the
close study of cell heterogeneity, and the manner in which individual
cells can go awry as they transition to diseased states. "In our
analysis of live single cells we can quantify significant variation from
cell to cell under the same conditions," says Meldrum.
The group used Cell-CT to examine 150 cells in each of three
specific categories: normal, benign fibrocystic and malignant breast
epithelial. Controversy remains as to whether breast fibrosis, which may
result from hormonal changes, is a normal condition or an early
harbinger of malignancy. The condition occurs when ligaments, scars,
supportive tissue or other fibrous tissue become more prominent in the
breast than fatty tissue.
Cell-CT is a new kind of microscope, able to image cells in
three-dimensions, using a technique called optical projection
tomography. Cell-CT operates much like a normal CT scanner, though it
uses visible photons of light, rather than X-rays. Cells prepared for
observation are not placed on slides, but are instead suspended in gel
and injected through a micro-capillary tube that permits multiple
imaging in 360 degrees.
The scanning process produces hundreds of thin slices through the
cell. These sections, or tomographs, are reassembled through computer
software, forming a detailed 3-D portrait. Movies of cells seen in
rotation brilliantly reveal shape asymmetries, a particularly useful
tool for disease diagnosis.
The three cell types examined in the study fell into four distinct
nuclear shape categories. Category 1 cell nuclei were slender, with
marked concavity. Category 2 cells had a slight concavity and were
bulky. Based on these shapes, the first two categories are termed
mushroom cap morphology. (The Category 2 mushroom cap morphology was the
most common nuclear form seen in all three cell types.) Category 3
nuclei were mostly convex in shape, while Category 4 nuclei were
irregular and distorted in shape.
Importantly, cells drawn from the cancerous cell line showed the
largest fraction of irregular, Category 4 and Category 2 nuclei and the
smallest fraction of nuclei with a Category 3 convex shape. The
malignant cells also displayed the greatest shape heterogeneity within
Category 4. The fibrocystic cell sample contained the largest fraction
of Category 3 and the lowest fraction of Category 1 nuclei. The largest
overall shape heterogeneity with respect to the four shape categories
occurred in the normal cells.
Cell and nuclear volume were observed to increase as one moves from
normal to fibrocystic to malignant cells, though fibrocystic cells had,
on average, the largest nucleus-to-cytoplasm volume. Textural
distinctions among cells and arrangement of chromatin were also
observed. In all, the team computed 42 distinct 3-D morphological and
textural descriptors of cellular and nuclear structure. Cell-CT
technology is able to resolve cell features down to less than a half
micron.
Study co-author Roger Johnson, Research Laboratory Manager at the
Center for Biosignatures Discovery Automation, stresses that the subtle
nuclear differences observed, particularly for the malignant cells,
would likely have been missed had the samples been examined with
conventional 2-D imagery. As a result, the architecture imaged with
Cell-CT supercedes the existing nuclear grades established for cancer
diagnosis using a microscope.
Though much progress has been made in understanding the
transformation of cells from normal to diseased states, patient outcomes
for many forms of cancer remain discouragingly poor. Many believe a new
paradigm for investigating such cancers will need to be established,
and the field has drawn interested researches from diverse disciplines.
Paul Davies, another co-author of the current study is a physicist and
cosmologist in ASU's College of Liberal Arts and Sciences and part of a
new National Cancer Institute funded consortium, devoted to studying the
physical science of cancer: "We expect that insights and methods drawn
from physical science will lead to radical new ideas for understanding
and tackling cancer," says Davies.
The group's results provide a new window on the variations of
nuclear structure that often signal cell malignancy. The unparalleled
structural details produced by Cell-CT promise to dramatically improve
3-D nuclear morphometry, leading to a sensitive and specific nuclear
grade classification for breast cancer diagnosis.
