Introduction

Prostate ductal adenocarcinoma is a rare histology found in 0.4–0.8% of all prostate cancers and is treated in the same way as acinar adenocarcinoma, but it is more likely to metastasize and recur than acinar adenocarcinoma and also shows poorer prognosis [1]. There have been few reports of solitary recurrence in the anterior urethra rather than the anastomosis after radical prostatectomy.

We herein describe a rare case of prostate ductal adenocarcinoma that developed a late recurrence in the anterior urethra 13 years after radical prostatectomy.

Case presentation

A 73-year-old Asian Japanese man was referred to our department for the further analysis of gross hematuria. He had no particular family history and complications. And he had no habit of smoking and drinking. Magnetic resonance imaging diffusion-weighted imaging (MRI–DWI) showed a high density in his prostate, and cystoscopy revealed a papillary tumor in his prostatic urethra (Fig. 1). His serum prostate-specific antigen (PSA) level was 15.9 ng/mL. Based on these findings, a prostate needle biopsy and transurethral resection were performed. At the time of admission, he had no particular physical and laboratory findings including CBC, renal function, liver function etc. The prostate needle biopsy showed no malignancy, and the resected tumor showed ductal prostate carcinoma without acinar adenocarcinoma. Subsequently, radical prostatectomy with lymph node resection was performed. The resected specimens showed a Gleason score of 4 + 4 = 8 adenocarcinoma without any findings of ductal cancer and no lymph node metastases. The PSA level decreased to < 0.010 ng/mL 3 months after prostatectomy.

Fig. 1
figure 1

Magnetic resonance imaging showed prostate cancer by diffusion-weighted images (a axial) and T2-weighted images (b axial, c sagittal) The yellow arrows show the target tumor

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A total of 2 years after the prostatectomy, his serum PSA level gradually increased to 0.159 ng/mL, and early salvage radiation therapy was performed (64.8 Gy/36 fr). And no adjuvant hormonal treatment was performed. Three years after salvage radiation therapy, his serum PSA level increased again (0.07 ng/mL); however, both CT and cystoscopy showed no recurrence. Due to the long doubling time of his serum PSA level, both computed tomography (CT) and cystoscopy were performed without further treatment. Thirteen years after the initial prostatectomy procedure, cystoscopy revealed a papillary tumor in the anterior urethra (Fig. 2). His serum PSA level was 0.400 ng/mL, and urinary cytology revealed negative findings. Transurethral resection was performed to confirm the pathological findings. The resected specimens showed findings similar to those of his past prostatectomy specimens and positive findings on PSA staining. Based on these findings, the urethral papillary tumor was diagnosed as a metastasis of prostate ductal carcinoma (Fig. 3a, b).

Fig. 2
figure 2

Cytoscopic images of the anterior urethra

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Fig. 3
figure 3

a The main histological features of the tumor in the prostatic urethra, b positive immunohistochemical staining for PSA

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After transurethral resection, the patient’s serum PSA level decreased to < 0.010 ng/mL (Fig. 4). At 6 months after transurethral resection, the patient was free of recurrence. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET)–CT is not currently available in Japanese.

Fig. 4
figure 4

The clinical course and PSA transition

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Discussion

This case was initially diagnosed with prostate ductal adenocarcinoma, undergoing radical prostatectomy that revealed a Gleason score of 8 without lymph node metastasis. Despite early success in lowering PSA levels and salvage radiation for rising PSA, a metastatic tumor in the anterior urethra was identified 13 years later.

Prostate ductal carcinoma is a relatively rare histology, accounting for 0.2–0.8% of all prostate cancers [1]. Compared with adenocarcinoma, it is characterized by a higher rate of metastatic recurrence and worse prognosis [2], a higher rate of positive margins after prostatectomy [3], and a higher rate of genetic mutations [4].

Urethral carcinoma is the most common malignancy that causes urethral tumors, with only a few reports of prostate cancer described [5]. Prostate ductal carcinoma often shows tubular, papillary, or cribriform structures that are histopathologically similar to those of urethral carcinoma, and PSA staining is useful for differentiating between the two [6]. In the present case, the possibility of urethral carcinoma could not be ruled out because of the presence of a papillary tumor; however, immunohistochemical staining was strongly positive for PSA, so a definitive diagnosis of prostate cancer was made.

Prostate cancer with solitary anterior urethral metastasis is rare, with only 19 reported cases. Among them, only three cases of solitary recurrence of radical prostatectomy to the urethra have been reported (Table 1) [7,8,9]. Two cases had positive margins at the time of prostatectomy, while one case reported by Merrett et al. recurred in the anterior urethra despite a negative margin. All patients had a history of transurethral resection.

Table 1 Reported cases of urethral metastasis from prostate cancer after radical prostatectomy
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This is the first case of late recurrence 13 years after surgery. Although the mechanism of urethral solitary recurrence of prostate cancer is still unknown, it has been proposed that prostate cancer tumors grow in the urethra after it has been damaged by catheterization [10]. In the present study, all patients had a history of transurethral resection; thus, a history of transurethral surgery might have been associated with recurrence in this case. Previous reports showed that urethral recurrence after radical prostatectomy without metastasis in other organs had a good prognosis [7, 9, 11,12,13,14]. Local recurrence after radical prostatectomy is most common at the vesicourethral anastomosis, and there is no established treatment for solitary urethral recurrence [15]. Although total urethral resection is considered a reliable treatment for urethral recurrence, it requires urinary diversion. Considering the patient’s age of 86 at the time of recurrence, we evaluated that removing the urethra with urinary diversion in an elderly patient can pose challenges due to the risk of serious complications.

Generally, prostate ductal carcinoma is unlikely to induce increases in PSA levels [16]. In the present case, the PSA level decreased after resection of the anterior urethral tumor, but it was necessary to continue regular imaging follow-up using cystoscopy and CT in addition to serum PSA level monitoring.

Conclusion

We encountered a rare case of prostate ductal carcinoma recurrence 13 years after the initial treatment.