**2. Technological innovations and classifications**

RCC tends to invade the renal venous system, forming a thrombus that invades the IVC and even involving the right atrium [2]. RN with tumor thrombectomy is the standard approach for treating such challenging cases. The grading system based on tumor thrombus height was created to determine surgical strategies. As early as 1987, the Mayo Clinic had adopted the "NEVES grading." Level I is defined as a tumor thrombus that is <2 cm apart from the orificium of the renal vein. Level II is defined as a tumor thrombus extending to the IVC >2 cm above the renal vein but below the hepatic veins. Level III is defined as a tumor thrombus that extends above the hepatic veins but below the diaphragm. Level IV is defined as a tumor thrombus located above the diaphragm. Surgical strategies are varied in corresponding levels. Traction of the liver is required in levels I to II. Turning-up the liver, blocking-up vessels located below the diaphragm, and clamping the portal vein are required in levels II to III. The establishment of an extracorporeal circulation is necessary in levels III and IV [8]. In 2002, the University of Miami divided level III tumor thrombus into four categories ulteriorly, which corresponded to diverse surgical strategies [9]. However, the most classic guideline is the "5-level classification" of a tumor thrombus, which was proposed by the Mayo Clinic in 2004 [10]. Idiographic grading standards and surgical strategies are shown in **Table 1**.

Nevertheless, these grading systems are completely based on the experience of open surgery. Since Skinner first reported the open surgery of IVC tumor thrombectomy in 1972 [11], the technique of IVC tumor thrombectomy has been improving continuously. Some scholars had attempted to accomplish these surgeries with laparoscope in 2002 [12, 13]. In 2011, Abaza first reported on robot-assisted IVC tumor thrombus extraction [14]. In recent years, several medical centers have investigated the safety and feasibility of robot-assisted laparoscopic IVC thrombectomy (RAL-IVCTE) [15–18]. Based on the anatomic characteristics of RCC, we


**Table 1.** The grading standards and surgical strategies tumor thrombus.

reported the particular steps of robot-assisted surgery and concluded that RAL-IVCTE is safe, and different sides require different techniques [18]. Gu and colleagues performed a retrospective comparison between open and robotic surgeries in IVC thrombus. The study indicated that level I–II IVC tumor thrombectomy performed with robot-assisted surgery resulted in better perioperative periodical outcomes and analogous oncological outcomes compared with open surgery, marking that such surgery has entered the era of mini-traumatic surgery [19].
