Sunday, October 12, 2008

Neoplasms: Excerpt 5

Neoplasms: principles of development and diversity was published October 1, 2008. In the next few blogs, I will provide some short excerpts from the book.

Excerpt from Chapter 2 Carcinogenesis (Section 2.9: Tumor Dormancy):

Dormancy occurs when an established cancer (one that has passed through the stages of initiation, latency, and precancer) stops growing for a period of time. When people use the word dormancy, they are usually referring to one of three situations

Examples of tumor dormancy.

1. A patient has an invasive brain tumor and has refused any form of therapy. The tumor is followed by radiologic imaging at regular intervals. The tumor that had been growing suddenly ceases to grow, for several years, before resuming growth.

2. An invasive primary tumor is excised. There is no evidence at the time of excision that the tumor has metastasized. Several years later, the patient develops clinically obvious metastatic lesions in multiple organs.

3. A patient with carcinoma is diagnosed with cancer. The cancer is staged. Several regional lymph nodes (near the primary cancer) are found to have small deposits of metastatic cancer. The patient is treated with excision of the primary tumor followed by intensive chemotherapy. Several years later, the patient develops clinically obvious metastatic lesions in multiple organs.

In each of these cases, the tumor undergoes a period of dormancy. Biologically, each instance of dormancy is a distinctly different process. In the first instance, an entire tumor ceased growth. In the second instance, occult metastases (i.e., metastases that were not evident at the time of diagnosis) persisted without noticeable growth for some period of time before becoming clinically obvious. In third instance, a patient with known metastatic cancer was treated with systemic chemotherapy. The metastatic lesions survived chemotherapy and eventually grew to become clinically detectable masses.

The phenomenon known as tumor dormancy probably represents several different processes that have the same observed outcome: growth cessation and growth renewal of a formerly growing neoplasm. In the case of the second instance (occult metastases growing after a period of time), we can speculate that the process of metastasis selected for a cell that escaped from a primary tumor and settled in a distant anatomic site. The selection process for a metastatic cell may not have favored a cell that was particularly well equipped to grow into a thriving clone. It is likely that most metastatic cells die without producing clinically detectable metastatic lesions. The emergence of a growing metastatic subclone may have required multiple successful generations of very slow growth, during which a fast-growing descendant cell was selected.

(to be continued)

The full table of contents is available. In the next few days, I will continue to discuss content from Neoplasms in my blogs.

-Jules Berman

Key words: tumors, tumour, neoplasms, neoplasia, carcinogenesis, tumor development, cancer research, neoplastic development, precancer preneoplasia, preneoplastic

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