Splenic metastasis is unusual and well known as the spleen is rarely subject to malignancy due to its special anatomical architecture and microenvironment.20 The clinical situation and tumoral spreading behavior can help predict the possibility of splenic metastasis at an advanced stage of cancer.9
Some authors reported the presence of splenic metastasis in unexpected, controlled cases. Antonio et al. reported on a patient who developed spleen metastases years after surgical treatment and months after chemotherapy for metastases. The splenic lesion was detected incidentally via surveillance studies. This case highlights that splenic metastasis, although rare, may occur even in a patient with a locoregional and systemically controlled primary cancer.21
After an extensive review of the literature, we found a total of 67 reports of unusual splenic metastases that were related to various primary cancers; in around 40 of them, the primary malignancy was colon cancer.
Recently, in 2022, Linxian et al. analyzed 40 previously published cases (22 men and 18 women) where the metastasis originated from colon cancer. The mean age of the patients was 64 years, ranging from 33 to 84 years. Constitutionally, in almost all patients, splenic metastases were detected during the postoperative follow-up period by imaging.15
Our literature review showed that the majority of patients with solitary splenic metastases do not have any specific clinical manifestations, generally presenting with, for example, asymptomatic or nonspecific abdominal pain. For clinical diagnosis, a good clinical history, tumor markers, multimodal radiological examinations, and microscopic histopathology are required. The justifiable pathway of treatment involves splenectomy followed by comprehensive, agreed-upon follow-up electives and appointments.7
The prerequisites for early detection and clinical guidance are advanced modalities in diagnostic imaging techniques for metastatic disease.4 Cross-sectional imaging CT/MRI can show potentially malignant features. It can mimic other lesions with no lymphadenopathy. Biopsy carries a high risk of splenic bleeding and a risk for tumor development and spontaneous rupture.14
Histological examination remains the gold standard for diagnosis15 as we saw in almost all published cases. However, the management of rare cases of metastases at uncommon sites is not well defined. Some authors, such as Xu et al., stated that such cases can be a form of disease recurrence. As per the report by Xu et al., their patient underwent a successful resection of low rectal cancer; 5 years later, a follow-up CT scan revealed a tumor in the spleen, considered an isolated metastasis, with no other abdominal metastasis.5 Since the time interval between the diagnosis of primary cancer and splenic metastasis may be very long, it is necessary to monitor the recurrence of cancer after primary treatment.9
An FDG-PET scan can provide a useful diagnostic value in conjunction with pathological results in evaluating tumor staging. The utility of FDG-PET for metastasis detection is emphasized in cases of primary malignancies of the endocrine glands, such as thyroid carcinoma.6
Theoretically, we can depend on other supportive laboratory parameters to confirm recurrence, such as an elevated serum (CEA) value.8 A recent study investigated a new marker used to confirm the colonic origin of metastases, called special AT-rich sequence-binding protein 2 (SATB2), which could retain its expression at the metastatic sites. SATB2 was totally concordant between primary colorectal cancers and their paired metastatic sites, with a perfect level of agreement. Thus, it could be considered an accurate diagnostic marker. The combination of SATB2 and caudal-type homeobox 2 (CDX2) has the highest sensitivity and specificity in the detection of colorectal cancer.21
Apart from splenomegaly or abdominal pain,9 splenic metastasis can lead to other complications, such as superimposed abscess formation or even splenic rupture. Kunishige et al. reported a case of gas-producing splenic abscess in 2021. The patient’s condition improved with antibiotics and splenic drainage. In 2019, Kazuhisa et al. reported on a case of splenic rupture detected via CT. Coil embolization of the splenic artery was performed, following which the patient’s condition improved.18
Therefore, for effective management, splenectomy is currently the most effective potential treatment for solitary splenic metastases. Careful consideration of surgical indications is required, as splenic metastasis is often accompanied by multiorgan metastasis and dissemination.
A major cancer treatment method is the “wait-and-see” approach using chemotherapy. Radiotherapy is not commonly used. Karakushi et al. (2020) treated splenic metastasis with the “wait-and-see” strategy with chemotherapy. Depending on the response, complete imaging and intensive multidisciplinary therapy could be a treatment option for disseminated or splenic metastases.11 In one case, with chemotherapy over 10 months of follow-up visits in an oncology outpatient clinic, no evidence of recurrence or metastasis was observed.12 Therefore, regarding outcomes, with follow-up after splenectomy and frequent cycles of chemotherapy, the patient will be alive, well, and without evidence of disease.17
Thus far, evaluation criteria in solid splenic tumors should be achieved by multidisciplinary management. Some authors have mentioned that the combined strategy of splenectomy and adjuvant chemotherapy is the optimal therapeutic approach to prolong survival and ameliorate the disease.13