Characteristic pattern of human prostatic growth with age*

Shu-Jie XIA¹, Xiao-Xin XU², Jian-Bao TENG³ , Chun-Xiao XU³, Xiao-Da TANG¹

Asian J Androl 2002 Dec; 4: 269-271            

Keywords: prostatic hypertrophy; age factor; B-ultrasonography; androgen

Abstract

Aim: To study the characteristic pattern of the age-related growth of the human prostate gland. Methods: The volume (weight) of the prostate in 1,601 males, aged from newborn to 92 years, was determined by B-ultrasonography. Results: Prostatic volume determination by B-ultrasonography in 1601 males (1301 normal subjects and 300 BPH patients) pointed out that the age-stratified growth of human prostate could be categorized into 4 life stages: (1) the first slow growing phase (from newborn to 9 years): the prostate grows slowly at a rate of 0.14 g per year; (2) the first rapid growing phase (from 10 to 30 years): the prostate grows at a rate of 0.84 g per year; (3) the second slow growing phase (from 30 to 50 years), the prostate grows at a rate of 0.21 g per year; (4) the second rapid growing phase (from 50 to 90 years): the prostate grows at one of the following rates: in one group the growth rate is of 0.50 g per year and in the other 1.20 g per year, leading to benign prostatic hyperplasia (BPH). Conclusion: The volumes of the prostate are different in different age groups and it grows with age at different rates in four life phases. The prostate growth in phases can be expressed by the following equation: Y=19.36+1.36X'^-0.58X'²+ 0.33X'³, where Y = prostate volume, X = age (up to 70 years), X'= (X-35.5)/10.

The distribution characteristic of prostate diseases with aging makes urologists concentrate on the relationship between prostate growth and age. Hiraoka et al [1] studied this correlation in 25 subjects aged from fetuses of 22 weeks to old men of 92 years, suggesting that the enlargement of human prostate gland was a natural history from genesis and development to physio-pathological hyperplasia. Berry [2] reviewed 10 relevant articles involving more than 1 000 autopsy specimens of prostate; he believed that the human prostate gland experienced two growth stages: (1) the rapid growth stage: between 10 and 30 years of age, the prostate gland was growing at a rate of 1.60 g per year; (2) the slow growth stage: between 30 and 90 years, the prostatic weight was increased by 0.40 g per year and might come up to BPH. Gu et al [3] demonstrated that the human prostatic weight of people, aged 40~70 years, displayed a trend of increase with age in both the urban and rural populations, the mean growth rate in the urban population being 0.19 g per year.

Although the relationship between prostate growth and age has been attached much importance, reports regarding the natural course of prostatic growth in different age groups are scarce. The present study was designed to investigate the natural prostatic growth with age and to yield the normal values of prostate size in different age groups.

2 Materials and methods

From Apr 1987 to Mar 2001, in 1301 urban males, from newborns to 92 year old men, enrolled in the national project for men's health, quantitative evaluation of the prostatic volume/weight (1 mL of prostatic tissue weighed approximately 1 g) by B-ultrasonography (SSD 502 and 650, Aloka, Japan) was performed. They were apparently healthy and had no any complain in regard to the urogenital system. At the same time in 300 BPH patients undergoing prostatectomy, preoperative ultrasound-scanning of the prostate was also carried out; the prostatectomy specimens were weighed to correct the results of B-ultrasonography as previously reported [4]. The lateral, the antero-posterior and the supero-inferior diameters of the prostate were measured and the volume of prostate was then calculated by the equation, V= p/6lateral diameteranter-posterior diametersupero-inferior diameter. Subjects were divided into groups by 10-year age intervals.

3 Results

Prostatic volume determination by B-ultrasonography in 1601 males (1301 normal subjects and 300 BPH patients) pointed out that the age-stratified growth of human prostate could be categorize into 4 life stages: (1) the first slow growing phase (from newborn to 9 years): the prostate grows slowly at a rate of 0.14 g per year; (2) the first rapid growing phase (from 10 to 30 years): the prostate grows at a rate of 0.84 g per year; (3) the second slow growing phase (from 30 to 50 years), the prostate grows at a rate of 0.21 g per year; (4) the second rapid growing phase (from 50 to 90 years): in one group the growth rate is of 0.50 g per year and in the other 1.20 g per year, leading to benign prostatic hyperplasia (BPH) (Tables 1, 2). The prostate growth in phases can be expressed by the following equation: Y=19.36+1.36X'^-0.58X'²+ 0.33X'³, where Y = prostate volume, X = age (up to 70 years), X'= (X-35.5)/10.

Table 1. Prostatic volume in different age groups (mean SD).

Table 2. Prostatic volume in BPH patients above 50 years old (mL). *International prostate symptom score.

4 Discussion

AM Willams et al [5] indicated that overall prostatic growth rate was 2.36 ?3.52 mL per year and that the growth was increasing with age with the peak of 4.154.98 mL per year at the age of 56~65 years and declined rapidly with the further advancement of age. Based on autopsy data, Berry et al [2] described the normal value of prostate volume, which is 20.06.0 g in subjects aged 21 to 30 years without BPH.

Prostate is an androgen-dependent organ [6-8]. The changes in the production of androgen in different age groups may be the basis of the age difference in prostatic growth rate. McNeal [9] proposed a three-process theory about the genesis and development of BPH: (1) the prophase, with a diffuse growth of the gland, (2) the metaphase, with hyperplasia of the lesser tubercle, (3) the anaphase, with hypertrophy of the node. The unceasing accumulation of the hypertrophic nodes leads to BPH in aging. J T Isaacs et al [10] put forward the following hypotheses in regard to the development of BPH: (1) the dihydrotestosterone (DHT) hypothesis: a shift in prostatic androgen metabolism occurs with aging, leading to an abnormal accumulation of DHT, (2) the embryonic reawakening theory: a change in the prostatic stromal-epithelial interaction occurs in aging, leading to induction of prostatic growth, and (3) the stem cell theory: an increase in the number of prostatic stem cell and/or an increase in the clonal expanding of the stem cells into amplifying and transit cells occur in aging. Sensibarb [11] reported that homeostasis in prostate was maintained by a complex interplay between the opposing actions of cell proliferation and cell death; growth regulatory factors that promote or inhibit cell proliferation and promote cell death have been identified in the prostate and an imbalance between the net cell proliferation and death rates determined by the growth regulatory factors, might result in abnormal growth leading to BPH. However the definitive mechanism of human prostate growth may be the results of interaction of multiple factors [12].

This study revealed the natural course of human prostatic age-stratified growth, the normal prostate volumes in different age groups and the equation of human prostatic growth, thus providing basic data for the researches on prostate and the diagnosis and treatment of BPH. Results suggest that individuals with a prostatic growth rate of 0.50 g ~1.20 g per year fall into it high-risk group of BPH. Our results are in close accordance with those of other authors [2, 3, 13], indicating a similarity of prostatic growth pattern with different populations. The reason for the second rapid growing phase in individuals after 50 years old when their blood testosterone levels begin to drop awaits further investigation.

References

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Correspondence to: Dr. Shu-Jie XIA, Department of Urology, Shanghai First People's Hospital, 85 Wujin Road, Shanghai 200080, China.

Tel: +86-21-6324 0090 Ext 5712, Fax: +86-21-6324 0825

E-mail: XSJ@citiz.net

* Presented at the First Asia-Pacific Forum on Andrology, 17-21 Oct 2002, Shanghai, China

Received 2002-09-03      Accepted 2002-12-01