Relationship between mammographic and histological risk factors for breast cancer

BACKGROUND

Information on breast cancer risk can be obtained both from the histological appearance of the breast epithelium in biopsy specimens and from the pattern of parenchymal densities in the breast revealed by mammography. It is not understood, however, how parenchymal densities influence breast cancer risk or whether these densities are associated with histological risk factors.

PURPOSE

We have estimated, in a large cohort of women, the relative risk of detecting carcinoma in situ, atypical hyperplasia, hyperplasia without atypia, or nonproliferative disease in biopsy specimens from women with different extents of mammographic density. We also examined the association between these histological classifications and radiological features present specifically at the biopsy site.

METHODS

The source of study material was a population of women aged 40-49 years who were enrolled in the Canadian National Breast Screening Study (NBSS). Mammograms from women who had undergone a biopsy (n = 441) and from a comparison group of women (n = 501) randomly selected from the mammography arm of the NBSS were classified according to the extent of mammographic density. The corresponding histological slides were independently classified by a review pathologist.

RESULTS

Compared with women showing no mammographic densities, women with the most extensive densities (i.e., occupying greater than 75% of the breast volume) had a 9.7 times greater risk of developing carcinoma in situ or atypical hyperplasia (95% confidence interval [CI] = 1.75-53.97), a 12.2 times greater risk of developing hyperplasia without atypia (95% CI = 2.97-50.14), and a 3.1 times greater risk of developing non-proliferative disease (95% CI = 1.20-8.11). The gradients in risk were not monotonic across the five classifications of mammographic density. The association could not be explained by the presence of mammographic densities at the biopsy site, but calcification at the biopsy site was strongly associated with high-risk histological changes (relative risk = 24; 95% CI = 5.0-156.0).

CONCLUSIONS

These results suggest that the radiological patterns referred to as mammographic dysplasia may influence breast cancer risk by virtue of their association with high-risk histological changes in the breast epithelium.

IMPLICATIONS

Identification of the factors responsible for high-risk histological changes may offer new insights into the etiology of breast cancer and potentially lead to the development of methods for its prevention.

Modulation of the human sperm acrosome reaction by effectors of the adenylate cyclase/cyclic AMP second-messenger pathway

The acrosome reaction of spermatozoa appears to be analogous to various somatic cell exocytotic events which involve cascade reactions, i.e., transmission of an external signal across the cell membrane resulting in activation of an "amplifier" enzyme and the generation of a second messenger. Using a synchronous acrosome reaction system (De Jonge et al., J. Androl., 10:232-239, '89a), it was found that analogues of the second-messenger cAMP, dibutyryl cAMP (dbcAMP) and 8-bromo cAMP, stimulated the acrosome reaction of capacitated spermatozoa. Additionally, treatment of spermatozoa with either xanthine or non-xanthine phosphodiesterase inhibitors induced a significant (P less than 0.05) increase in the percent acrosome reaction after a period of capacitation in comparison to untreated controls. These results indicate that analogues of cAMP or inhibitors which prevent cAMP hydrolysis can induce the human sperm acrosome reaction. Subsequent experiments were conducted to test whether the amplifier enzyme in the cascade reaction, adenylate cyclase, has a role in the acrosome reaction. Forskolin, an adenylate cyclase stimulator, caused a significant (P less than 0.01) increase in the percent acrosome reaction in comparison to controls. Modulators of adenylate cyclase--adenosine, 2'-0-methyladenosine, and 2',3'-dideoxyadenosine--significantly (P less than 0.01) inhibited the forskolin-induced acrosome reaction. dbcAMP was able to overcome the inhibition by adenosine. Two inhibitors of protein kinase A, the Walsh inhibitor and H-8, caused a significant (P less than 0.01) inhibition of the dbcAMP-induced acrosome reaction. Finally, in the absence of extracellular calcium, dbcAMP induced a significant (P less than 0.01) increase in the acrosome reaction in contrast to A23187. These results suggest that: 1) a molecular mechanism for the human sperm acrosome reaction involves the cAMP second-messenger system; i.e., activation of adenylate cyclase, the amplifier enzyme that produces cAMP, production of cAMP as a second messenger, and activation of cAMP-dependent kinase A; and that 2) activation of adenylate cyclase occurs after calcium influx.

Effect of phorbol diesters, synthetic diacylglycerols, and a protein kinase C inhibitor on the human sperm acrosome reaction

The acrosome reaction of spermatozoa may be analogous to various somatic cell exocytotic events that incorporate cascade reactions. One such cascade system involves the hydrolysis of a membrane-bound phospholipid; generation of the intracellular second messenger, diacylglycerol; and activation of protein kinase C, followed by the phosphorylation of a number of intracellular proteins. Stimulators of protein kinase C, phorbol diesters and synthetic diacylglycerols, were evaluated to determine if this system functions in the human sperm acrosome reaction. Phorbol 12-myristate 13-acetate and 4 beta-phorbol 12,13-didecanoate caused a significant (P less than 0.01) increase in the acrosome reaction of capacitated spermatozoa. Conversely, an inactive phorbol diester had no significant (P greater than 0.05) stimulatory effect on the acrosome reaction. The synthetic diacylglycerols, 1-oleoyl-2-acetyl-sn-glycerol, 1,2-dioctanoyl-sn-glycerol, and 1,2-dioleoyl-sn-glycerol caused a significant (P less than 0.01) increase in the acrosome reaction of capacitated spermatozoa, and to a similar extent as the phorbol diesters. A nonactivating isomer of 1,2-dioleoyl-sn-glycerol, 1,3-diolein, had no significant (P greater than 0.05) stimulatory effect on the acrosome reaction. Protein kinase C activation is a diacylglycerol-dependent and Ca2(+)-dependent process, and stimulation of the acrosome reaction by 1,2-dioctanoyl-sn-glycerol required the presence of calcium ions in the capacitation medium. An inhibitor of protein kinase C, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), prevented the diacylglycerol-induced acrosome reaction (P less than 0.01). These results support the hypothesis that protein kinase C, via activation by the intracellular second messenger diacylglycerol, has a role in the human sperm acrosome reaction.

Inhibition of the human sperm acrosome reaction by a high molecular weight factor from human seminal plasma

Human seminal plasma possesses a factor (acrosome reaction-inhibitory factor) that is precipitated by high speed centrifugation and that inhibits the ionophore- and dbc AMP-induced acrosome reaction of capacitated human spermatozoa but only if it is added toward the end of the capacitation period. Acrosome reaction-inhibitory factor can be partially purified by cation exchange chromatography and appears to differ from another factor that can be obtained by ultracentrifugation of human seminal plasma and that prevents the fertilization of mouse gametes.