The present study has focused attention essentially on the Parsis, an ethnic group with high breast cancer incidence. We have investigated the potential use of prosomes, compared to Ki-67 and PCNA, as an additional cell proliferation marker. We also addressed the question whether or not breast tumors of Parsis differed in their DNA index and in the proportion of the S-phase fraction, compared to that of non-Parsi and European patients. We observed that the benign tumors of Parsis and non-Parsis were hyperdiploids, whereas in case of malignant tumors the Parsis showed essentially diploid characteristics while hyperdiploidy prevailed in the non-Parsis. Tetraploidy was seen as a common feature in the non-Parsis, whereas aneuploidy seemed to be the more common type in the Parsis. The cell cycle analysis also revealed some interesting differences between the cell proliferation compartments of these two populations. A high number of cells in G2+M and S-phases was seen for non-Parsi malignant tumors while only the S-phase had a large cell count in the Parsis malignant tumors. The malignant tumors of Parsis and non-Parsis showed, as would be expected, a high expression of Ki-67 in the proliferation compartment. Surprisingly high Ki-67 expression was also a feature seen in the benign tumors of Parsis only and not any other group. We observed that expression of Ki-67, a proliferation marker directly related to the degree of malignancy, paralleled that of prosomal protein expression. In addition the prosomal monoclonal antibodies appeared to be more sensitive than Ki-67 in detecting a larger quantum of cells in the proliferation compartment.

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