Metastatic gastric adenocarcinoma in prostate: A case report

Abstract

We report a case of prostate cancer metastasis from gastric cancer. Prostate metastasis of gastric cancer as the primary tumor is very rare, and it is difficult to distinguish using hematoxylin and eosin (HE) staining alone. Because immunohistochemistry is also necessary, it is important to accurately share patient information with pathologists.

1 Introduction

Prostate metastasis of gastric cancer is very rare, with only five cases reported, including the one reported here. It is difficult to distinguish metastasis of gastric cancer from primary prostate cancer using hematoxylin and eosin (HE) staining alone, and an accurate diagnosis may be difficult to make without information on patient’s medical history. Here, we report a case of prostate metastasis from gastric cancer that occurred during surveillance therapy for prostate cancer.

2 Case presentation

2.1 Case

In August 2015, a 71-year-old man presented with elevated prostate-specific antigen (PSA) level (4.3 ng/mL). Prostate biopsy, computed tomography (CT), and bone scintigraphy led to a diagnosis of prostate cancer with cT2aN0M0, Gleason score (GS) of 3 + 3 = 6. Simultaneously, he had advanced gastric cancer and underwent a total gastrectomy in December 2015. The pathological diagnosis was adenocarcinoma pT4aN0M0. He was started on S-1 as adjuvant chemotherapy but developed ileus after approximately 3 months of chemotherapy. Subsequently, the patient discontinued TS-1; however, no evidence of recurrence was present. Prostate cancer was under active surveillance because it was in the low-risk group of the NCCN guidelines, and the patient continued treatment for gastric cancer. In December 2020, follow-up computed tomography (CT) for gastric cancer revealed an abnormality of the prostate, and magnetic resonance imaging (MRI) revealed a suspicious finding of malignancy from the base of the prostate to the seminal vesicle ( Fig. 1 AB). At that time, his PSA was 5.94 ng/mL, which was not markedly elevated. In January 2021, a prostate biopsy was performed again under the suspicion of advanced prostate cancer. Prostate biopsy revealed adenocarcinoma, and immunohistochemistry was performed to differentiate between prostate and gastric cancers. The results demonstrated that the tumor cells were positive for CDX2, CK7, and CK20 and negative for PSA, leading to a diagnosis of gastric cancer recurrence ( Fig. 2 ). The patient resumed chemotherapy (S-1+oxaliplatin) for prostate metastasis from gastric cancer, and CT performed in January 2022 revealed shrinkage of the lesion ( Fig. 3 A). In 2023, peritoneal metastases appeared; however, the prostate lesion continued to reduce in size and was still undergoing treatment.