What are the similarities between benign and malignant growths?
Both benign and malignant growths are defined as abnormal growths of cells which leads to the cells becoming ‘immortal’ and growing uncontrollably outside of their naturally defined boundary. Benign and malignant cells are quite different, however: in order to avoid confusion, I will only use the term ‘cancer’ with malignant cells. They are both capable of undergoing differentation and anaplasia, which I’ll discuss below, and most of the time the type of growth can be diagnosed by examining the different features under the microscope. This is not always easy, however, as some tumours defy the normal set of rules applied in histopathology. I’ll also be referring to the differences in these two types of growths when it comes to rate of growth, their capability of invasion and metastasis and whether they are encapsulated or not.
What are the different types of tumours that exist?
As a general rule, benign tumours use the suffix ‘-oma’ and malignant cancers use either the suffix ‘-sarcoma’ or ‘carcinoma’. A table demonstrating the different types of both benign and malignant tumours is below. You may notice that not all tumours have both a benign and malignant name: some tumours are strictly malignant in nature.
Differentiation and Anaplasia
A handy rule to remember when looking at cancer is as follows: Differentiation and anaplasia have an inverse relationship with one another: the more differentiated a tumour is, the less anaplastic it is, and vice versa.
Differentiation refers to the structure of the tumour cells in comparison to the normal cells
around it. In general, benign tumours tend to be well-differentiated whereas malignant cancers are poorly differentiated. In order words, benign cells appear similar to that of the surrounding normal structures, however, malignant cells often appear strikingly different to the normal cells around them. The case alongside is unusual as it is a malignant tumour (squamous cell carcinoma which affects the top layers of the skin), however the cells appear similar throughout. The importance of differentiation is that the more closely the cells resemble the normal structures, the better they are able to function as the surrounding cells would.
Anaplasia, conversely, refers to the cells becoming undifferentiated, or, in other words, more simplistic in structure. When this happens, the
cells lose the capacity to function like their neighbouring cells and they tend to have a less clearly-defined boundary, like the picture above demonstrates. Anaplastic cells, like the ones shown alongside within lymphoma, are typically associated with malignant cancers.
Invasion and Metastasis
The reason why many people sigh with relief when they hear that the tumour is ‘benign’ is that these types of tumours tend to stay in one location only and do not cause damage elsewhere. The significance of this fact is treatments of chemotherapy and/or surgery are more likely to rid the person of the tumour if it is only in one place. Malignant cancers, on the other hand, often have the tendency to metastasize, and the process is discussed more thoroughly in Invasion and Metastasis.
Capsules in Tumours
A key hint when looking for benign tumours is to look for capsules. Cancers don’t tend to have these features. An example of a benign, encapsulated tumour is shown alongside.
Rate of Growth
It is a general rule of thumb that benign tumours tend to develop slowly, whereas malignant cancers are more aggressive in nature. This is not always true, however: some types of cancers have both a chronic and an acute stage; in lymphoma, for example, the chronic stage acts slowly for years and then may suddenly become more acu