These discoveries resulted from years of laboratory work, including careful examinations of tumors grown in mice.

Megan Sweet, a biology graduate student at Virginia Tech, spends much of her time preparing very thin slices of tumor tissue. Inside a metal cold-storage chamber, she carefully adjusts a mounted tumor, roughly the size of a pinky fingernail, against a sharp blade.

“It’s all about fine-tuning and making sure you get even slices,” said Sweet, who studies biological sciences.

As the blade moves through the tissue, it produces a steady, rhythmic cutting sound.

“This is the hardest and most time-consuming part,” Sweet said. “But it’s also kind of meditative.”

Each piece is cut thin enough to allow light to pass through. Sweet then transfers the delicate tissue to glass slides and stains selected cellular structures, making them easier to distinguish under a powerful microscope.

The process involves repeatedly cutting, staining, examining, and comparing samples. Although arduous, the research is helping scientists understand why some tumors are much more dangerous than others.

A Virginia Tech team has published research shedding new light on how cancer develops and progresses. Their findings, published in Proceedings of the National Academy of Sciences along with additional research earlier this year, focus on the role of abnormal chromosome numbers and cancer cell size.

How Chromosomal Errors Can Promote Cancer

Most healthy cells in the human body are diploid, meaning they contain two complete sets of chromosomes—one inherited from each parent.

Under normal conditions, these cells divide to produce new cells with the same chromosome arrangement. In some cases, however, something goes wrong during cell division, leaving cells with an abnormal number of chromosomes.

These errors can accumulate if they are passed on during subsequent cell divisions. Such changes are one pathway through which cancer can develop.

For the past five years, Sweet and fellow graduate student Matt Bloomfield have worked with cell biologist Daniela Cimini to study cells with abnormal chromosome numbers, a common feature of cancer.

To examine the effects of these abnormalities, Cimini’s team engineered diploid cancer cells to duplicate their chromosomes without completing cell division.

The result was a type of cell known as a tetraploid cell. These cells contain four complete sets of chromosomes instead of the usual two.

Tetraploid cells are not limited to laboratory experiments. They can also appear during the development of human tumors, and their presence is associated with cancer progression and poor patient outcomes.

Cancer Cells Recruit Healthy Tissue to Support Tumor Growth

Scientists have long known that tetraploid cells can make tumors more aggressive. What remained unclear was how these cells contributed to cancer growth.

Sweet and Bloomfield compared tumors that developed from regular diploid cancer cells with tumors that developed from tetraploid cancer cells.

The experiment produced unexpected results.

As the mice’s tumors grew, the percentage of tetraploid cells actually decreased. Despite that reduction, the tumors continued to grow rapidly and reached a significant size.

Researchers found that tetraploid cancer cells promote the recruitment of stromal cells. These non-cancerous connective tissue cells provide structural support and appear to create an environment favorable for further tumor development.

“The presence of even a small fraction of these tetraploid cells can promote the recruitment of extra non-cancerous cells that support further tumor progression,” Dr. Sweet said.

The discovery reveals a previously unrecognized mechanism through which abnormal cancer cells can promote tumor growth, even when they make up only a small portion of a tumor.

Smaller Tetraploid Cancer Cells May Be More Aggressive

Separate research revealed another unexpected relationship between tetraploid cells and cancer aggressiveness.

Bloomfield initially investigated the physical characteristics of tetraploid cells. After creating tetraploid cells from human cancer cells and establishing colonies derived from individual cells, he noticed that the resulting groups were not all the same size.

Because tetraploid cells contain twice the normal number of chromosome sets, the researchers expected them to be about twice the size of diploid cells.

Instead, some cells were 25–30% smaller than expected.

Even more surprisingly, these smaller cells were more capable of forming aggressive tumors than the larger cells.

“The smaller clones are more aggressive,” Bloomfield said. “They grow faster, are more invasive, and are more resistant to common anti-cancer and stress-inducing drugs.”

Further experiments in mice confirmed these observations. Tumors containing small tetraploid cells often grew faster than tumors containing large cells.

This pattern was not limited to one type of cancer. The researchers observed similar results in colorectal and breast cancer cells, suggesting that the relationship between tetraploid cell size and tumor aggressiveness may span multiple cancers.

Cancer Cell Size May Help Predict Patient Survival

The researchers next investigated whether the same relationship appeared in human cancers.

They analyzed information from The Cancer Genome Atlas, a large collection of detailed data from thousands of cancer patient samples.

The results showed that, in several types of cancer, smaller tetraploid cells were associated with poorer prognosis and lower survival rates.

This suggests that measuring the size of abnormal cancer cells may provide valuable information about how aggressively tumors behave.

“We already knew that tetraploidy could make cells more tumorigenic, but now we found that taking cell size into account allows us to more accurately predict tumor formation potential,” Cimini said.

The discovery adds an important dimension to scientists’ understanding of cancer. Abnormal chromosome numbers have long been associated with risky tumor behavior, but the new research shows that cell size may provide additional clues about a cancer’s potential to grow and metastasize.

The research team plans to investigate the biological mechanisms responsible for these effects in greater detail while continuing to examine human cancer data.

For Sweet, that means more time in the laboratory, carefully cutting and analyzing small sections of tumor tissue in search of answers to one of the most important questions in cancer biology.