Cancer cells exhibit distinct visual differences when compared to healthy cells. These distinctions are fundamental for understanding cancer progression and are frequently used in diagnosis, allowing for their identification and characterization.
Distinctive Features of Cancer Cells
Cancer cells display irregularities in their size and shape, a characteristic known as pleomorphism, where cells within the same population show considerable variation. Some cancer cells may appear significantly larger than normal cells, while others might be smaller, and their overall forms can be highly abnormal or contoured.
The nucleus of a cancer cell undergoes changes, becoming enlarged and irregular in shape. It may acquire grooves, folds, or indentations, and its volume and density can vary. Within this altered nucleus, nucleoli—structures involved in ribosome production—become more prominent, increased in number, and can even appear enlarged and irregular with sharp projections.
The ratio of the nucleus to the cytoplasm, known as the nuclear-to-cytoplasmic ratio, is increased in cancer cells, meaning the nucleus takes up a disproportionately larger amount of the cell’s total volume. Chromatin, the complex of DNA and proteins within the nucleus, also shows abnormalities, transforming from a finely granular, evenly distributed pattern in normal cells into irregular clumps with varying sizes and shapes. This aggregation of abnormal chromatin can adhere to the inner surface of the nuclear membrane.
The cytoplasm, the material surrounding the nucleus, is reduced in volume in cancer cells and can exhibit abnormal features. It may appear intensely colored or, conversely, pale, and can contain new structures or show the disappearance of normal ones. The granular endoplasmic reticulum, an organelle involved in protein synthesis, may appear simplified, fragmented, and degranulated, sometimes losing its connections with mitochondria.
Beyond individual cell characteristics, cancer cells disrupt normal tissue architecture. Unlike healthy cells that form organized, uniform layers with strong cell-to-cell connections, cancer cells grow in disordered patterns and do not form uniform monolayers. They can lose the surface molecules that help normal cells adhere to each other and to the surrounding extracellular matrix, which contributes to their ability to break away and invade surrounding tissues.
Cancer cells also exhibit increased and abnormal mitotic activity, reflecting their uncontrolled division. Normal cell division, or mitosis, is a precise process, but in cancer, atypical mitotic figures are observed. These can include defects in the mitotic spindle, resulting in unusual structures such as tripolar or quadrupolar asters and asymmetrical divisions, where genetic material is unevenly distributed to daughter cells.
Observing Cellular Changes for Diagnosis
The visual distinctions of cancer cells are routinely used in medical diagnosis. The process begins with a biopsy, where a small tissue sample is obtained from the suspicious area.
Once collected, the tissue sample undergoes specific preparation. It is fixed using chemical or physical procedures to preserve the cells and their structures. Following fixation, the tissue is embedded, sliced into very thin sections, and then stained to highlight cellular details. Hematoxylin and Eosin (H&E) staining is a common technique, where hematoxylin stains cell nuclei blue or purple, and eosin stains the cytoplasm and extracellular matrix pink or red, allowing for clear visualization of cellular morphology.
A pathologist, a medical doctor specializing in disease diagnosis through tissue examination, analyzes these stained tissue sections under a microscope. They meticulously look for the distinctive features of cancer cells, such as irregular nuclear shapes, prominent nucleoli, and altered cellular organization. The identification of these specific morphological changes, combined with other observations like the presence of atypical mitotic figures, enables the pathologist to make a diagnosis of cancer.
The Biological Basis of Altered Appearance
The altered appearance of cancer cells stems from fundamental changes in their biological processes. A primary underlying reason is uncontrolled cell division, where cancer cells proliferate rapidly and without the normal regulatory signals that govern healthy cell growth. This unregulated expansion leads to an accumulation of abnormal cell populations that do not adhere to the body’s usual tissue organization.
These changes in cell behavior are driven by genetic mutations, which are alterations in the DNA of the cells. These mutations can affect genes that normally regulate cell growth, division, and programmed cell death. For example, a faulty version of the p53 protein, which checks for DNA damage and initiates cell repair or death, can lead to cells accumulating more genetic errors and growing faster.
Cancer cells exhibit a loss of differentiation, meaning they lose their specialized functions and revert to a more primitive or less organized state. Normal cells mature and specialize to perform specific roles within tissues and organs. In contrast, cancer cells may not mature properly, and their rapid division can prevent them from developing their full specialized characteristics, leading to structural and functional abnormalities.