Lung cancer can metastasize to any organ. Major sites of metastases include brain, bone, and adrenal glands, other organs are involved usually in late stage of the disease. Among different lung cancer types, there are also preferential metastatic sites, such as liver metastases from small cell lung cancer (SCLC) and brain metastases from SCLC or adenocarcinoma[9]. Cases of metastases to the kidney are relatively rare, and are mainly reported in single cases[10]. In current study about renal metastatic cancer, the lung is the most common source of metastases, followed by colorectal, gastric and breast malignancies, and most patients do not have specific urologic symptoms [11]. Interestingly, more than two-thirds of patients develop isolated renal metastases, but most eventually develop metastases in other organs [12, 13]. Considering that the kidney is a highly vascularized organ, metastatic infiltration is likely due to arterial embolization[14].
Distinguishing between primary and secondary tumors of the kidney is essential to guide treatment and prevent unnecessary surgery. However, the clinical presentation of patients with renal metastatic carcinoma may be similar to that of renal cell carcinoma, presenting as a single mass with hematuria. Therefore, the initial diagnosis of renal metastases usually comes from routine imaging, but the final diagnosis needs to rely on pathological diagnosis[2]. Aspiration biopsy is often used to diagnose renal metastases before surgery[15]and in half of the six cases in this study also used. Because of the low degree of differentiation of tumor cells in the primary foci of lung cancer metastasizing to the kidney and the relatively small and atypical morphology of the tissue in the biopsy specimens, they easily overlap with primary renal tumors such as renal cell carcinoma and uremic syndrome. Therefore, it is necessary to take a detailed medical history and make full use of immunohistochemical techniques to help us make a differential diagnosis, which is very important for clinical treatment. Therefore, clinical data, radiological data, histological correlation of the primary tumor and immunohistochemical findings help to determine the correct pathological diagnosis[16].
In these six cases, the patients were all male and the mean age was 62 years, which is consistent with other reports in the literature [17]. In our study, Case 1 with a poorly differentiated adenocarcinoma of the lung, received radiotherapy and chemotherapy, and underwent radical nephrectomy. Later, he developed brain metastases and dead of disease. Case 2 with moderately differentiated adenocarcinoma of the lung received partial nephrectomy, and only chemotherapy was performed, but the follow-up is still underway. Case 3 with lung small cell carcinoma had the shortest time to metastasize to the kidney. After receiving radiotherapy and chemotherapy, then brain metastases occurred, and dead of disease. Case 4 with poorly differentiated squamous cell carcinoma of the lung received radiotherapy and immunotherapy without surgery, and finally dead of disease. Case 5 and Case 6 were both with moderately differentiated adenocarcinomas of the lung, of which case 6 underwent partial nephrectomy, both received radiotherapy and immunotherapy, and are currently being followed up. From the clinicopathological results, we found that the degree of differentiation of tumor cells after metastasis from lung cancer to the kidney did not change significantly, which may be because the degree of differentiation of the primary tumor was mainly low differentiation, but the Ki67 of tumor cells decreased after metastasis, suggesting that the proliferation activity of tumor decreased, which may be related to clinical treatment. Four of these cases were lung adenocarcinomas, which is consistent with the incidence of different histological types of lung cancer that adenocarcinomas are more common than other types.. From the clinical data about metastases to the kidney from primary lung cancer, the clinical symptoms of the six patients were not obvious, and only two patients had hematuria, mainly due to imaging findings. Lung squamous cell carcinoma and lung small cell carcinoma metastasized to the kidney in a relatively short time, while the metastatic time of lung adenocarcinoma was related to its degree of differentiation. The worse the differentiation, the faster the metastasis. Three of the patients underwent nephrectomy, one with laparoscopic radical nephrectomy and two with laparoscopic partial nephrectomy. For patients with solitary renal metastases and reported in the literature, nephrectomy can significantly prolong the survival time of patients [2], but it is impossible to prove whether nephrectomy has a positive effect on prognosis in this study due to limited data.
The current primary goal of systemic therapy in patients with metastatic NSCLC is to reduce the symptom burden of the cancer and improve survival while aiming to improve quality of life[9]. Platinum-based combination chemotherapy regimens (eg, carboplatin and paclitaxel or carboplatin and pemetrexed) have been shown to improve survival compared with single-agent chemotherapy, and in some patients, surgery, radiation, or both may be required to treat symptoms[18]. Notably, immunotherapy is one of the major advances in the treatment of advanced tumors in recent years, and non-small cell lung cancer (NSCLC) is one of the cancers that benefits the most from this approach. Currently, the only validated companion diagnostic test for first-line immunotherapy in patients with metastatic NSCLC is the expression of programmed death ligand 1 (PD-L1) in tumor tissue[19]. Small cell lung cancer (SCLC) has different pathological, clinical and molecular features from non-small cell lung cancer. SCLC has a high metastatic potential, resulting in poor clinical prognosis. Concurrent chemoradiotherapy is currently the standard treatment for SCLC, and the FDA has also accelerated approval of nivolumab for the third-line treatment of metastatic SCLC[20]. All patients in this study received chemotherapy, some patients chose to combine radiotherapy and chemotherapy, and some patients received immunotherapy combined with chemotherapy, which may be related to the high expression of PD-L1. It has been reported in the literature that SBRT is well tolerated and safe for metastatic renal cancer, and it can provide good symptom relief and early local control[21].
In this study, we showed six cases of lung cancer metastasis to the kidney from different tissue subtypes, and described and analyzed their clinical features, pathological features, treatment methods and prognosis, in order to provide help for the pathological diagnosis and clinical treatment of lung cancer with renal metastasis in the future.