ON THE MECHANISM OF THE FORMATION OF METASTASES IN MALIGNANT TUMORS : AN EXPERIMENTAL STUDY

Primary tumor associated macrophages activate programs of invasion and dormancy in disseminating tumor cells

Metastases are initiated by disseminated tumor cells (DTCs) that colonize distant organs. Growing evidence suggests that the microenvironment of the primary tumor primes DTCs for dormant or proliferative fates. However, the manner in which this occurs remains poorly understood. Here, using the Window for High-Resolution Intravital Imaging of the Lung (WHRIL), we study the live lung longitudinally and follow the fate of individual DTCs that spontaneously disseminate from orthotopic breast tumors. We find that spontaneously DTCs have increased levels of retention, increased speed of extravasation, and greater survival after extravasation, compared to experimentally metastasized tumor cells. Detailed analysis reveals that a subset of macrophages within the primary tumor induces a pro-dissemination and pro-dormancy DTC phenotype. Our work provides insight into how specific primary tumor microenvironments prime a subpopulation of cells for expression of proteins associated with dissemination and dormancy.

Prostate cancer screening and treatment: where have we come from and where are we going?

OBJECTIVE

To evaluate the current prostate cancer screening and treatment paradigm in light of recently published long-term results of major screening and treatment trials.

METHODS

Historical review of the evolution of the diagnosis and treatment of prostate cancer followed by a detailed summary of the findings and differences among the three major screening trials and the three major treatment trials.

RESULTS

Prostate-specific antigen (PSA) testing can identify clinically significant prostate cancer and has produced a significant stage shift and is the likely explanation for the decline in prostate cancer mortality. Unfortunately, PSA testing predominantly identifies low-grade disease that is unlikely to progress during a patient's lifetime leading to substantial diagnosis of indolent disease. Treatment with radical prostatectomy (RP) appears to benefit primarily younger men (aged <65 years) with intermediate-grade disease. Too few men with low-grade disease benefit from RP to justify intervening in all. Unfortunately, high-grade prostate cancer often progresses despite surgery and radiation.

CONCLUSION

The primary PSA testing paradigm is wrong. Rather than attempting to identify all prostate cancers as early as possible, testing objectives should shift towards identifying men likely to harbour clinically significant disease. These are the men who appear to benefit from early diagnosis and intervention, including the earlier use of antiandrogen therapy prior to widespread metastases.

What is the risk posed by prostate cancer?

Prostate cancer carries an extraordinarily varied prognosis. Previously, most men presented with clinical symptoms often succumbed to their disease several years following treatment with hormonal manipulation. With the advent of prostate-specific antigen (PSA) testing, most men are now diagnosed with localized, well- to moderately differentiated disease. The most powerful predictor of long-term outcome is the Gleason score, followed by tumor volume. Over the past two decades, changes in the interpretation of Gleason patterns have resulted in the reclassification of many well-differentiated tumors as higher grade tumors. Men with well-differentiated disease have an excellent prognosis and often survive 10-20 years without intervention. Conversely, men with poorly differentiated disease often succumb to their cancer within a decade. PSA can estimate tumor volume, but poorly differentiated disease may not produce much PSA. We are unable to predict accurately the risk posed by a specific prostate cancer.

The dissemination of cancer cells during operative procedures

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TUMOR INOCULATION INTO ORGANS AND THE ANALOGY BETWEEN HUMAN CANCER AND THE TUMORS OF WHITE MICE AND WHITE RATS

The analysis of the experiments described above indicates that tumors of the white rat or white mouse inoculated into parenchymatous organs acquire a different biological character from those inoculated subcutaneously. The latter are a great deal more benign in their behavior than human cancer or spontaneous tumors in the same species of animals. Tumors inoculated into organs, on the other hand, are quite identical in their biological behavior with the malignant tumors of animal and man. A conclusion must then be drawn, even a priori, that the method of inoculation into organs is a very important aid in the experimental investigation of cancer. It is true that the method is a great deal more complicated and time-consuming than the ordinary subcutaneous inoculation. The subcutaneous method is satisfactory for a number of cancer problems. One of these is the study of general susceptibility and resistance of the organism of the host to the inoculation of the tumors, and this is a subject of paramount importance in cancer research. On the other hand, the investigations of the writer (10) have shown that an animal may be susceptible to a subcutaneous inoculation of a certain tumor and resist the inoculation of the same tumor into the testicle. Undoubtedly this method of inoculation will reveal the existence of a number of other phenomena. The discovery of specific therapeutic measures is certainly the greatest problem in cancer research. A great deal of work has been done already on the subject, and the latest investigations of Wassermann on the chemotherapy of experimental tumors seem to be of great promise. But here also the therapeutic methods must be tried on animals in which the inoculations of tumor cells have been made into parenchymatous organs before the growths thus treated will have any analogy to human cancer. In this connection one must bear in mind the fact that all the empirical so-called specific cancer remedies, which are continually being devised, are usually successful in treating localized skin cancers and fail utterly in the malignant growths of the internal organs. It is comparatively easy to produce a localized necrosis and softening in a circumscribed growth of the skin and subcutaneous tissue, but whether the same result will be produced on a diffuse and better nourished tumor growing inside of a parenchymatous organ cannot be decided a priori. To determine this it is necessary to have experimental proof on animals in which the tumor was inoculated into organs.