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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 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)—a specialized instrument capable of imaging cells in vivid 3D with
true isotropic resolution. The technology permits the examination of subtle
cellular details inaccessible by more conventional forms of microscopy that are
inherently 2D.
The group’s findings appear in PLoS
ONE.
The 3D movie images of cells observed in the study reveal numerous telltale
traces of their condition as normal or aberrant. 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, one in eight 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 3D 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 3D 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 2D 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, said: “We expect that insights and methods drawn from
physical science will lead to radical new ideas for understanding and tackling
cancer.”
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 3D nuclear
morphometry, leading to a sensitive and specific nuclear grade classification
for breast cancer diagnosis.
