Chen M E, Troncoso P, Johnston D, Tang K, Babaian R J
Department of Urology, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Urology. 1999 Apr;53(4):764-8. doi: 10.1016/s0090-4295(98)00574-3.
It has been suggested that the lower detection rate for cancer in large prostates is due to the smaller proportion of tissue sampled. To examine this hypothesis, we evaluated whole-mount radical prostatectomy specimens in which the volume of cancer had been determined. We correlated cancer volume to overall gland volume. In addition, we performed stochastic computer simulations of parasagittal sextant biopsies on the same group of radical prostatectomy specimens. We correlated the likelihood of a positive cancer biopsy simulation with tumor volume and gland size.
Six hundred seven tumor foci from 180 serially sectioned whole-mount prostatectomy specimens were mapped and digitized. Tumor volume was calculated by a step-section planimetry algorithm. Before sectioning, each gland was weighed. Systematic parasagittal sextant biopsies were computer simulated for each case. For each prostate, 40 simulations were performed, with random variations in biopsy location programmed for each run. Overall cancer detection by biopsy was considered positive if 90% of the 40 simulation runs were positive for cancer. Chi-square tests were used to evaluate statistical significance.
Small-volume cancers (0.5 cc or less) were twice as frequent in large glands greater than 50 g (P = 0.03). These small-volume tumors comprised 33% (13 of 40) of cancers in prostates greater than 50 g, 16% (5 of 31) in glands less than 30 g, and 14% (15 of 109) in glands 30 to 50 g. The rate of positive sextant biopsy simulation was lower in glands greater than 50 g than in glands 50 g or less (48% versus 67%, P<0.03). Smaller cancers were much less likely to be detected in the simulations. The simulation detection rate for cancers 0.5 cc or less was 18% (6 of 33), compared with a detection rate of 73% (107 of 147) for cancers greater than 0.5 cc (P<0.00001).
The observed lower cancer detection rate in large glands is a result of the higher proportion of low-volume cancers in these glands. This suggests that large prostates are more likely to be biopsied because of an elevated prostate-specific antigen value resulting from benign elements of the gland and not from a significant cancer. Increasing the number of cores solely to compensate for increased prostate size risks a disproportionate increased detection of small-volume tumors with a low clinical likelihood of progression.
有人提出，大前列腺癌的检出率较低是由于所取组织的比例较小。为验证这一假说，我们评估了已确定癌体积的全层根治性前列腺切除术标本。我们将癌体积与整个腺体体积进行关联。此外，我们对同一组根治性前列腺切除术标本进行矢状旁六分区活检的随机计算机模拟。我们将癌活检模拟阳性的可能性与肿瘤体积和腺体大小进行关联。
对180个连续切片的全层前列腺切除术标本中的607个肿瘤病灶进行定位和数字化处理。通过阶梯切片面积测量算法计算肿瘤体积。在切片前，对每个腺体进行称重。对每个病例进行矢状旁六分区活检的系统计算机模拟。对于每个前列腺，进行40次模拟，每次运行时活检位置随机变化。如果40次模拟运行中有90%的结果为癌阳性，则认为活检总体癌检测为阳性。采用卡方检验评估统计学意义。
在大于50克的大腺体中，小体积癌（0.5立方厘米或更小）的出现频率是其他腺体的两倍（P = 0.03）。这些小体积肿瘤在大于50克的前列腺癌中占33%（40个中的13个），在小于30克的腺体中占16%（31个中的5个），在30至50克的腺体中占14%（109个中的15个）。大于50克的腺体中矢状旁六分区活检模拟阳性率低于50克及以下的腺体（48%对67%，P<0.03）。在模拟中，较小的癌更不容易被检测到。0.5立方厘米或更小的癌的模拟检测率为18%（33个中的6个），而大于0.5立方厘米的癌的检测率为73%（147个中的107个）（P<0.00001）。
在大腺体中观察到的较低癌检测率是由于这些腺体中低体积癌的比例较高。这表明大前列腺更容易接受活检是因为腺体良性成分导致前列腺特异性抗原值升高，而非源于显著的癌。单纯为了补偿前列腺增大而增加活检针数有风险，即不成比例地增加对临床进展可能性低的小体积肿瘤的检测。
