Background
In primary tumors, distant metastasis is the most important predictive factor of prognosis in many malignant tumors. The common route of tumor metastasis involves tumor cell invasion and penetration lymphatics and/or blood vessels, subsequently disseminating to distant organs. Furthermore, angiogenesis within the tumor is crucial for tumor growth and metastasis, whereas lymphangiogenesis is a critical factor for tumor progression [
1‐
3]. Growth of the primary tumor mass requires angiogenesis, and new microvessels within tumors are predominant sites for tumor cell entry into circulation due to lack of intact basement membrane and a tight junction between endothelial cells [
4]. Vascular endothelial growth factors family members stimulate lymphangiogenesis in tumors thereby enhancing metastatic processes [
2,
5].
Xp11.2 translocation renal cell carcinoma (Xp11.2 translocation RCC) is a rare subtype of renal cell carcinoma (RCC), characterized by several different chromosomal translocations involving Xp11.2 and the formation of TFE3 fusion genes, followed by overexpression of TFE3 protein [
6]. Patients with Xp11.2 translocation RCC have often presented with advanced stages and demonstrated an invasive clinical course and poor prognosis [
7]. In addition, Xp11.2 translocation RCC patients exhibited moderate prolonged enhancement under dynamic contrast-enhanced computed tomography and were more susceptible to lymph node metastasis than those with common subtypes of RCC [
8,
9]. Recent studies based on microvessel density (MVD), microvessel area (MVA), lymph vessel density (LVD), and lymph vessel density (LVA) have revealed that micro-angiogenesis and lymphangiogenesis are significant prognostic predictors of RCC or clear cell renal cell carcinoma (ccRCC) [
10‐
13]. However, the role of micro-angiogenesis and lymphangiogenesis within Xp11.2 translocation RCC has not been fully elucidated. Microvessel density (MVD) or LVD, parameter designed to quantify the extent of tumor vascularization or lymphatics, refers to the number of small blood or lymph vessels per tumor area, while MVA or LVA is described as the total lumen area of small or lymph vessels. Nevertheless, due to limited direct studies on Xp11.2 translocation RCC, we quantified micro-angiogenesis and lymphangiogenesis within Xp11.2 translocation RCC using the parameters including MVD, LVD, MVA, and LVA.
Herein, we purposed to explore the correlation between tumor-related microvascular or lymphatic quantitative parameters and the prognosis of Xp11.2 translocation RCC. Based on quantitatively analyzing the distribution of microvessels and lymphatics of Xp11.2 translocation RCC histologically, and comparing it with ccRCC.
Discussion
Angiogenesis and lymphangiogenesis within malignant tumors are crucial for tumor growth and metastasis [
1,
2]. Numerous studies have confirmed that tumor micro-angiogenesis and lymphangiogenesis could be effective prognostic predictors in many malignant tumors such as prostatic adenocarcinoma, thyroid cancer, and breast cancer [
16‐
18]. On the contrary, other studies based on meta-analysis showed that tumor micro-angiogenesis and lymphangiogenesis are not useful predictive factors for the prognosis in RCC [
19,
20]. However, Xp11.2 translocation RCC is a rare subtype of RCC, and its clinical outcome is significantly different from the common subtypes of RCC. The Xp11.2 translocation RCC has been noted to depict a wide variation in biological behavior and clinical outcome [
7]. Therefore, the role of micro-angiogenesis and lymphangiogenesis within Xp11.2 translocation RCC is imperative, and necessities further studies. Although this study has demonstrated that tumor-related microvascular and lymphatic parameters were not independent prognostic factors for Xp11.2 translocation RCC patients, we revealed that Xp11.2 translocation RCC is a highly vascularized solid RCC, which is characterized by rich lymph vessels in the peritumoral area. This valuable information may provide a histological theoretical basis for tumor metastatic pathways and thereby giving new strategies for treating Xp11.2 translocation RCC based on the tumor anti-angiogenic therapy theory.
The tumor micro-angiogenesis has been measured in several ways including MVD, MVA, quantifying tumor angiogenic molecules, microvessel invasion and assessing the presence of tumor-associated angiogenic receptors, while the lymphangiogenesis has been quantified using various methods such as LVD, LVA, lymphatic vessel invasion, and vascular endothelial growth factors family members [
10,
12,
21‐
23]. Currently, the MVD, MVA, LVD, and LVA have widely been used as measurement parameters for assessing micro-angiogenesis and lymphangiogenesis within RCC. In this context, we computed the microvessels and lymphatics within the Xp11.2 translocation RCC using MVD, MVA, LVD, and LVA. Previous studies have opined that there were many vascular markers such as factor VIII, CD31, CD34, and CD105 for marking microvessels endothelium in malignant tumors [
12]. Overall, findings from multiple studies have noted that CD34 expression exhibited no variation over time and thus better compared to several other markers for staining microvessels [
24,
25]. Herein, CD34 was used as the most suitable vascular markers for counting microvessels in Xp11.2 translocation RCC. Furthermore, other several lymphatic vessel markers namely D2–40, lymphatic vessel endothelial hyaluronan receptors, and vascular endothelial growth factor receptors are available for detecting lymphatic endothelium [
10,
17]. In particular, the D2–40 antibody was used to mark lymphatic vessels in this study due to its specificity for lymphatic vessels [
26].
Here, the prognostic value of MVD and MVA indicating the microvessels in RCC remained inconsistent and unclear. In another study by Sharma et al. reported that the MVD within RCC was not significantly correlated with tumor grade and stage, and thereby MVA appeared to be a good prognostic factor for RCC [
12]. Elsewhere, multiple studies demonstrated that MVD in RCC exhibited an inverse association with tumor aggressiveness [
24,
27], whereas other reports revealed no relationship between MVD and survival [
19,
20]. In this work, the intratumoral MVD and MVA were significantly associated with grade and stage of Xp11.2 translocation RCC. However, the intratumoral MVD and MVA were not independent prognostic factors for Xp11.2 translocation RCC. The discrepancy between the results of these studies could be attributed to various factors such as tumor vascular system complexity, pathological subtypes of RCC, sample size, selection of vascular markers, immunohistochemistry staining quality, and methods of microvessel count. Despite different kinds of research focused on the tumor micro-angiogenesis in RCC, the prognostic value of LVD and LVA for assessing the lymphangiogenesis in RCC are rarely studied. Moreover, Iwata et al. reported that both intratumoral and peritumoral LVD were not associated with the pathological features in RCC [
10]. On the other hand, a recent study has elucidated that the presence of intratumoral lymphatic vessels exhibited a significant correlation with distant metastasis and lymph node metastasis [
28]. In contrast, findings from our study demonstrated that peritumoral LVD or LVA of Xp11.2 translocation RCC was significantly associated with several pathological variables including pT stage, pN stage, cM stage, AJCC stage, and WHO/ISUP grade, while increased peritumoral LVD or LVA indicated a relationship with high pathological stage and increasing nuclear grade. Notably, pathological subtypes of RCC, sample size, immunohistochemistry staining quality, and methods of microvessel count may be major reasons why conclusions from the above studies were very different. Therefore, the role of tumor lymphangiogenesis in the intratumoral and peritumoral area of RCC necessitates further research.
To avoid the selection bias of different areas of the tumor examined under the microscope, we analyzed the intratumoral and peritumoral areas of Xp11.2 translocation RCC. The results revealed that MVD or MVA in the intratumoral area was significantly higher compared to that of the peritumoral area, which was inconsistent with the findings of Cao et al. [
29]. In particular, their study implied that the peritumoral area in ccRCC included considerably more microvessels. The inconsistency between these two studies is likely due to pathological subtypes of RCC and microvessel counting methods. Additionally, CSS in Xp11.2 translocation RCC patients were significantly longer in patients with low intratumoral MVD or MVA than in patients with high intratumoral MVD or MVA, which corresponded with the result of a previous study [
11]. Nevertheless, another recent study has revealed that high MVD was associated with longer survival, which contradicts the findings of our study [
13]. Conclusively, MVD or MVA in the intratumoral area plays a minimal role in predicting the prognosis for Xp11.2 translocation RCC, but it is not an independent prognostic factor for Xp11.2 translocation RCC. Compared with the tumor microvessels in intratumoral and peritumoral areas of Xp11.2 translocation RCC, the tumor lymphangiogenesis was significantly different between intratumoral area and peritumoral area of Xp11.2 translocation RCC. Besides, findings from this work indicated a predominance of D2–40 positive lymph vessels primarily in the peritumoral area of Xp11.2 translocation RCC, whereas only 9 (26.5%) cases depicted D2–40 positive lymph vessels in the intratumoral area of Xp11.2 translocation RCC. Recently, many studies have recorded intratumoral and peritumoral distribution of lymphatic vessels in RCC [
10,
28]. Interestingly, the distribution of lymphatic vessels in Xp11.2 translocation RCC was consistent with that of traditional RCC. High-tissue pressure in tumor interstitium could be the main reason why lymph vessels were not detected in the intratumoral area of RCC [
17]. Lastly, this study outlined that peritumoral LVD or LVA was not associated with CSS in patients with both low peritumoral LVD or LVA and high peritumoral LVD or LVA. However, previous reports indicated that RCC patients with low peritumoral LVD exhibited significantly shorter CSS [
30]. Surprisingly, the role of tumor lymphangiogenesis in RCC remains elusive, and hence further studies are indispensable.
There are some limitations in the study. The sample size was not enough large due to the low incidence of this rare disease, and the follow-up time for patients was relatively short. In addition, the criteria for defining microvessels need to be further clarified, whereas the counting method should be more objective, accurate, convenient and efficient.
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