Epidemiological studies have shown that the incidence of prostate cancer varies among different populations and Chinese men have among the lowest¹. The reason for these differences is unclear but theories have included environmental, genetic, dietary and hormonal factors^2-4. Furthermore, the incidence of prostate cancer is higher among Chinese immigrants to the United States when compared to cohorts in Shanghai, China⁵. Numerous reports have described the use of transrectal ultrasound guided prostate biopsy in the diagnosis of prostate cancer in Caucasian men, however; there exists no such data for Chinese men. To provide insight into this ethnic difference, we now report on our clinical experience for detecting prostate cancer using transrectal ultrasound guided prostate biopsies in Chinese American men.

A retrospective chart review of transrectal ultrasound guided prostate biopsies performed over a three and a half year period was conducted on a cohort of Chinese men residing in the United States who presented with an elevated PSA > 4.0 ng/ml, a suspicious DRE or an abnormal TRUS. A total of 265 men comprised this retrospective group. The ages ranged from 51 to 90 years with an average of 70.4 ± 6.7 years. PSA followed a normal distribution with an average of 9.72 ± 21.0 ng/ml. There were 161 suspicious digital rectal exams (61%) in this group. Prostate size was determined by transrectal ultrasound and ranged from 6.7 cc to 122 cc with an average of 32.7 ± 17.0 cc. Overall, 34 cancers were detected by TRUS/BX for a positive biopsy rate of 12.8%. This data is summarized in table 1.

Table 1 Summary of Clinical Data

From October 1994 to October 1995, 80 men with a suspicious DRE or an elevated PSA > 4.0 ng/ml were seen in consultation. All these men underwent a transrectal ultrasound guided prostate biopsy using a sextant pattern template. The age range was 44 to 82 with an average of 67.8 ± 6.9 years. PSA followed a normal distribution with an average of 8.1 ± 8.5 ng/ml. A total of 30 suspicious digital rectal examinations (37%) were found in this group. Prostate sizes ranged from 7.6 cc to 155 cc with an average of 27.9 ± 18.2 cc. Overall, 11 cancers were detected by TRUS/BX for a positive biopsy rate of 13.7%. This data is summarized in table 1.

Age, PSA, and PSAD as an independent factors were found to influence biopsy outcome (Students’ t-test t=2.18, 2.6, 3.46, respectively, p<.05). A suspicious DRE correlated with a positive biopsy (c²=3.71, p=.05), however, an abnormal TRUS exam did not (c²=0.19, p=.66).

Relative risk ratios for a positive biopsy were calculated and the results are summarized in table 2.

Table 2. Relative risk of an abnormal finding

In the United States, prostate cancer accounts for 28% of all non-cutaneous malignancies and is second only to lung cancer for the number of male cancer related deaths ⁶. By comparison, epidemiological studies have shown this tumor to be rare in China⁷. Some authors have suggested that the prevalence of latent prostate cancer remains the same regardless of ethnicity and that the prevalence of clinically significant prostate cancer is less in Chinese men⁸. Evidence for this racial difference was provided by an autopsy series which looked at the difference in the prevalence of latent prostate cancer between blacks and white men in the United States. They identified a subset of latent but infiltrative lesions in the black population which was not seen in the white population⁹. Akazaki also showed that this difference in latent infiltrative cancers also exists when comparing native Japanese men with the Issei (first generation Japanese immigrants) in Hawaii¹⁰. This was equated to the increased incidence of prostate cancer seen in the Issei. Nevertheless, why such a difference should exist remains an unanswered question and relatively little is known about prostate cancer in the Chinese population.

Over the past several years, improvements in our ability to detect prostate cancer has resulted in a flood of American men presenting to the urologist for evaluation. This is best evidenced by the growing numbers of men with the diagnosis of stage T1C prostate cancer undergoing radical prostatectomy. As a result, there now exists a large body of data on the application of PSA, DRE and TRUS in the diagnosis of prostate cancer. The gold standard used to make this diagnosis has been the prostate biopsy and the number of publications describing the relationships between PSA, DRE and TRUS used in conjunction with a prostate biopsy has been innumerable. However, the utility of applying these diagnostic techniques in the Chinese population is unascertained.

Recent work reported by Oesterling et. al. demonstrated that the age specific reference ranges for serum PSA is lower in Japanese men when compared to a Caucasian cohort in the United States¹¹. It was postulated that this difference may be due to an overall trend towards smaller prostate sizes in Japanese men. To date, there is little data on the clinical presentation and diagnosis of prostate cancer in the Chinese population.

In the past, this has been due to the relatively small numbers of Chinese men seen in prostate screening programs but this trend is likely to change given that the Asian community is one of the fastest growing ethnic groups in the country.

The current study describes the prostate biopsy outcome in a group of Chinese men living in the United States and compares the performance characteristics of PSA, DRE, TRUS and PSAD. These men were drawn from a referred population and have lived in the United States an average of 16.8 years. In the retrospective review which was initially carried out, we demonstrated a low positive biopsy rate of only 12.8% which gave impetus to the development of a prospective biopsy series using a sextant pattern biopsy method. This second series in turn found a similar positive biopsy rate of only 13.7%. In the literature, several studies performed on a mostly Caucasian non-screening cohort have reported positive biopsy rates of 31.5%^12,13. By comparison, it would appear that the positive biopsy rate in Chinese American men falls short despite having similar indications for a biopsy. This cannot be attributed to a younger age since the average age in this study was 69 years. Nor do we believe that this lower biopsy rate reflects difference in biopsy technique since sextant biopsies were performed and sextant biopsies have been shown to have as high a yield as any other technique¹⁴. Furthermore, given the smaller prostate sizes found in this study, it should be more likely that one detects a cancer if it was present¹⁵.

In our Chinese cohort, the relative risk of having an elevated PSA > 4, PSA > 10, suspicious DRE, and abnormal TRUS were calculated and interestingly, were all quite low. This was not surprising given the low prevalence of prostate cancer believed to exist in Chinese men and the low positive biopsy rate.

Our results lend credence to the epidemiologic evidence that there is a lower incidence of prostate cancer in Chinese men and call into question the application of these diagnostic techniques in the Chinese population and other racial groups which may have different presentations of prostate cancer. One must keep in mind that the laboratory reference ranges commonly used are based on studies in Caucasian men with a relatively low minority representation. These results also raise the possibility that the ethnic variance seen in prostate cancer may be secondary to different a biological behavior. Zhau et. al. has recently reported on several significant findings on the molecular aspects of prostate cancer in Chinese men¹⁶. Studies such as these may ultimately lead to novel and more effective therapies for prostate cancer.

The yield from a transrectal ultrasound guided prostate biopsies performed in Chinese American men are lower than Caucasian men of similar age and with similar PSA levels. This finding supports the epidemiological reports that Chinese men have a lower risk of prostate cancer. However, the incidence of prostate cancer based on prostate biopsy in this population was not insignificant (13.7%).

In addition, we found that a PSA > 10 had the highest relative risk ratio at 2.1 and thus was the best indication for prostate biopsy. This is followed by a suspicious digital rectal examination with a relative risk ratio of 1.9. Conversely, an abnormal transrectal ultrasound finding had the lowest relative risk ratio of only 1.1 and should not be used as an indication for a biopsy in this group of men.

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