IntroductionMetastasis in the testes is a relatively rare occurrence, accounting for only 0.02% to 2.5% of all testicular tumors and is more common in older individuals. Identifying the primary site of tumors that resemble those found in both the gastrointestinal tract (GIT) and testis can be challenging. This is where immunohistochemistry plays a crucial role in making an accurate diagnosis, leading to proper treatment.[1]While primary malignancies in the small intestine are uncommon, accounting for only about 2.3% of all malignancies in the digestive system and 0.42% of all malignancies, it is essential to recognize the rare subtypes, such as signet-ring cell carcinoma (SRCC). SRCC is typically found in the stomach, but it can also occur in other organs such as the pancreas, breasts, bladder, ovaries, esophagus, lungs, and large intestine.[2]This report highlights an unusual case of a 44-year-old male patient with signet-ring cell mucinous adenocarcinoma metastasis of unknown source in the right testis, possibly originating from the small intestine.case presentation :A 44-year-old male presented with right testicular swelling, heaviness, and weight loss for the past 3 months. He is a heavy smoker and non-alcoholic with no past medical, surgical, or family history. The physical examination was normal except for the painful testicular mass. Echography of the testis showed a solid mass measuring 10.5x8x6 cm in the right testicle with irregular borders and increased vascularity. A Computerized Tomography (CT) scan with contrast showed multiple metastases within the chest lymph nodes, ribs, liver, pancreas, adrenal glands, periaortic lymph nodes, axillary lymph nodes, and groin lymph nodes. Bone scintigraphy demonstrated abnormal accumulation of the radiotracer in the 2nd and 7th ribs, the head of the left humerus, and throughout the right femur. The previous tests assumed a primary testicular cancer with metastasis, although alpha-fetoprotein (AFP), lactate dehydrogenase (LDH), and human chorionic gonadotropin (HCG) were normal. The team excised the right painful testicle and sent it for pathological studies.Surprisingly, the pathology report of the right testicle came with a final diagnosis of testicular signet-ring cell carcinoma metastasis (Figure 1) with positive CK7, CK20, and CDX2 immunostains (Figure 2), which suggests a primary origin from either the stomach or small intestine. The upper and lower endoscopies with biopsies from the stomach and colons were normal. In line with the pathology report, the team suspected that the tumor was most likely from the small intestine. However, we could not confirm our suspicion due to the lack of equipment that can visualize the small intestine. Therefore, the primary origin of the tumor remains unknown.SRCC is a rare and aggressive type of cancer that can explain the presence of multiple metastatic lesions in this patient. So, no further evaluation was performed to look for other metastatic sites due to the critical condition of the patient at the time of presentation. And the team suggested FOLFOX chemotherapy treatment protocol, after ruling out the gastric origin and suspecting intestinal origin. Follow up is not yet reported.Figure 1: Proliferation of signet ring cells with the displacement of the nucleus to the side by intracellular mucin. With accumulation of extracellular mucin.Figure 2 A, B: CK20 Positive immunostain. C, D: CK7 Positive immunostain. E, F: CDX20 Positive Immunostain