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Indian Journal of Cancer, Vol. 48, No. 1, January-March, 2011, pp. 110 Letter to Editor New adjusted cut-off level for serum prostate specific antigen V Wiwanitkit Wiwanitkit House, Bangkhae, Bangkok-10160, Thailand Correspondence Address: Code Number: cn11018 Sir, Screening for prostate cancer is a big topic in preventive medicine. The prostate specific antigen (PSA) is a serum tumor marker that is known for its usefulness in screening prostate cancer. [1] Although it is a widely used tumor marker, its limitations can still be seen. [1] The diagnostic sensitivity of PSA for screening prostate cancer is of main concern. Here, the author tries to find an adjusted cut-off level for PSA, aiming at increasing the diagnostic sensitivity. The data from the previously published meta-analysis on PSA diagnostic property in Thailand were used as the primary data for further developing the new model. According to the previous work, from 1321 screened cases, there are 143 cancerous cases and the pooled sensitivity is equal to 95.8% based on the standard cut-off level for PSA, 4 ng/mL. [2] The author finds the confidence interval and point estimation for the competition rate (cancerous vs. noncancerous cases) in the screening positive cases. [3] The derived calculated results are used for further adjustment of the present cut-off point of PSA. The derived confidence interval and point estimation for the competition rate are equal to 0.43-0.53 and 0.50, respectively. The derive rates are used for further adjustment of PSA cut-off value and the new PSA cut-off level based on point estimation is equal to 2 ng/mL. When the upper limit of derived confidence interval is applied to get the best new adjusted PSA cut-off level, the new derived PSA cut-off level is equal to 1.88 ng/mL. Recently, it was proposed that the cut-off value of PSA at 2 ng/mL might be better than the classical one (4 ng/mL). [4] Here, the author performed a study to find new adjusted PSA cut-off level based on the meta-analyzed data on diagnostic property of PSA among Thai reports. [2] The data were from the single nation and derived from the same method and standard for laboratory analysis. [2] Of interest, the derived new cut-off level for PSA, based on calculated point estimation, is equal to that proposed by Hekal. [4] The author hereby proposes a new level of adjusted PSA cut-off value to be 1.88 ng/mL, which is expected to have a very high diagnostic property for screening prostate cancer. Further studies to verify this new proposed adjusted PSA cut off level are suggested. However, the limitation on application of the new derived adjusted PSA cut-off value should be mentioned. As shown in the Prostate Cancer Prevention Trial, 15% of men with PSA <4.0 ng/mL and normal digital rectal examination have biopsy-detected prostate cancer. Hence, it is needed to decrease PSA cut-off value for detecting prostate cancer. However, specific trade-offs of lowering PSA cut-off value should be discussed. One of them is the spoiled specificity and a consequent increase in further unnecessary biopsy. This might lead to further unnecessary diagnostic management for non malignant cases. In addition, lowering cut-off of PSA can result in increased screening cost.. Recent studies suggested that PSA derivatives (e.g. prostate specific antigen velocity (PSAV), prostate specific antigen density (PSAD)) are promising as a means to increase the specificity of screening for clinically significant prostate cancer. [5] Hence, more specific screening protocols including PSA velocity will help to reduce over-diagnosis of indolent tumor. References
Copyright 2011 - Indian Journal of Cancer |
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