BACKGROUND Multiple primary malignant neoplasms are not frequent but are increasing in incidence. Some of them are associated with genetic syndromes such as von Hippel-Lindau syndrome and Li-Fraumeni syndrome. Dedifferentiated liposarcoma is one of the rarest soft tissue tumors, and clear cell renal carcinoma is the most frequent kidney cancer. The concomitant presence of these tumors is extremely rare; however, some cases have been reported, none of them presenting with liposarcoma of the limbs. We report an interesting case of a patient with synchronous multiple primary tumors presenting with a very rare liposarcoma associated with renal cell carcinoma (a very rare association). A review of the literature and a collection of similar cases published previously are also provided. CASE PRESENTATION We report a case of a 62-year-old Hispanic man who presented to our institution with a left thigh mass compatible with dedifferentiated liposarcoma synchronous with metastatic clear cell renal carcinoma. Multiple treatment lines were provided with no response, with a further metastatic transformation. Genetic analysis by liquid biopsy showed some mutations that were not susceptible to targeted therapy. At the time of this report, the patient is undergoing palliative care because his nonresponsive metastatic disease persists. CONCLUSIONS We present the first reported case of clear cell renal carcinoma synchronous with dedifferentiated liposarcoma of a limb. The association between renal cell carcinoma and dedifferentiated liposarcoma is unusual, and there are few reports of this presentation in the literature. More research about these tumors along with genetic tests needs to be performed to seek a better understanding of the fundamental basis of this rare association.

中文翻译：

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透明细胞肾癌并发未分化脂肪肉瘤：一例并文献复习。

背景技术多种原发性恶性肿瘤并不常见，但发病率正在增加。其中一些与遗传综合症有关，例如冯·希佩尔·林道综合症和李·弗劳梅尼综合症。去分化脂肪肉瘤是最罕见的软组织肿瘤之一，而透明细胞肾癌是最常见的肾癌。这些肿瘤并存的情况极为罕见。然而，已经报道了一些病例，没有一个病例出现四肢脂肪肉瘤。我们报道了一个有趣的病例，该患者患有同步性多发原发性肿瘤，并伴有与肾细胞癌相关的非常罕见的脂肪肉瘤（一种非常罕见的关联）。还提供了文献回顾和以前发表的类似案例的集合。病例介绍我们报告了一例62岁的西班牙裔男子，他向我们的机构就诊，左大腿肿块与去分化脂肪肉瘤相容，并伴有转移性透明细胞肾癌。提供了多个无反应的治疗株，并进一步转移。通过液体活检进行的遗传分析显示，某些突变不易接受靶向治疗。在撰写本报告时，患者正在接受姑息治疗，因为他的无反应性转移性疾病持续存在。结论我们介绍了第一例报告的透明细胞肾癌合并肢体去分化脂肪肉瘤的病例。肾细胞癌与去分化的脂肪肉瘤之间的关联是罕见的，文献中对此报道的报道很少。