Chapter 2 and 3:THE NATURE OF CANCER & TUMOR VIRUSES
Presenter: Radina P. Soebiyanto
Date of Lecture: May 21, 2007
Scribe: Jayant Avva
Date Posted by Scribe: May 22, 2007
Chapter 2 deals with the nature of cancer. Studying cancer statistics, especially the cancer death rates over the last 50 years, gives us an understanding of how complex the disease is. Morphological characteristics of cancer cells, as well as a step-by-step description of cancer progression from normal cells to invasive carcinoma, helps us look at the several dimensions underlying this complexity. Additionally, abnormal cellular features such as hyperplasia, metaplasia and dysplasia qualify various cancer phenotypes.
Tumor classification into carcinomas, sarcomas, neuroectodermal tumors as well as hematopoietic malignancies is done based on the tissue of origin. Each of these categories has specific cytological features and encompasses different sub-categories.
An overview of how normal cells become cancerous involves the conversion of proto-oncogenes into oncogenes. Moreover, cancerous tumors can be either monoclonal or polyclonal. Several statistics in the textbook show the importance of various mutagens, and the environment in general, in cancer proliferation.
Chapter 3 deals with Tumor viruses. Viruses have a specific structure that was discussed in the presentation. Virus cycles can be either temperate or virulent. Moreover the virus can be categorized based on how it carries its genetic content- as either a DNA virus or an RNA virus. The replication cycle of DNA viruses is usually virulent and the host cell is destroyed. The Rouse sarcoma virus (an RNA virus or a retrovirus) was a key turning point in tumor virus study, and helped researchers realize that the key to cancer was hidden at the cellular level. Tumor viruses can be classified into acquired-oncogene bearing, non-oncogene bearing and naturally-oncogene bearing.
There were several salient points that were discussed during the presentation. When going over the contact inhibition present in normal cells, it was noted that normal (non-pathological) fibroblasts could also grow on top of one another. However, the growth will not be to the extent of cancerous cells that form a focus. In other words, while the contact inhibition explanation in the textbook was sound in theory- it wasn’t as black and white in practice.
Other discussion points were:
• Fibroblasts and their exact nature.
• The Ames test for finding out whether certain mutagens were carcinogens or not. There were surprising findings here, showing us that many carcinogens are naturally occurring as toxic compounds in vegetables.
• A promising new area of cancer research dealing with the causal role of inflammation in many cancers.
• A question on whether leukemia occurs in the bone marrow or not was also discussed- with the final consensus that there is no way of knowing any different.
• Oncogenes are not inherited, though tumor suppressor genes are.