In the present case, immunohistochemical staining was performed for CK7, Vimentin, CD10, and EPO. The results were consistent with a diagnosis of chRCC according to the relevant reports and distinguished the condition from both ccRCC and renal oncocytoma [12,13,14,15]. In addition, plasma from the tumor cells was also EPO-positive. In combination with the patient’s recovery from “PV”, we confirmed that his erythrocytosis was caused by chRCC due to EPO production.
According to the patient’s medical history of erythrocytosis, we speculated that his renal tumor had a certain volume 9 years ago but was likely concealed by the patient’s symptoms of splenomegaly and failed to draw the attention of the physician. As a result, the patient was misdiagnosed with PV without any imaging examinations. During the subsequent 9 years, even though his abdomen was progressively swelling, the patient did not have any imaging examinations because the swelling was considered to be due to splenomegaly.
Renal artery embolization (RAE) was performed before radical nephrectomy in this case. During the surgery, we observed an abundant and complex blood supply traveling through the distended vessels on the surface of the tumor; however, the intraoperative blood loss was controlled within 500 mL without blood transfusion. There were also no complications caused by preoperative RAE, such as small groin hematomas or post-infarction syndromes including nausea or flank pain, as mentioned in a previous report [16].
It has been reported that RCC is the most common cancer causing erythrocytosis [8], especially the ccRCC subtype [8, 17]; other subtypes are rarely reported. Paraneoplastic syndromes of erythrocytosis have never been reported in chRCC. In addition, the facts that the chRCC occurred at such a giant volume and at such a young age without any metastasis, necrosis, or recurrence and was misdiagnosed as PV for 9 years make this case fairly unique.
As has been reported, secondary erythrocytosis occurs when factors outside of the bone marrow, such as tumors or other abnormal organs, stimulate EPO production [18]. To distinguish primary and secondary conditions, “no cause of secondary erythrocytosis” was added to the diagnosis criteria for the clinical practice guidelines of PV [19]. In recent years, it has generally been accepted that the JAK2 mutation presents in most PV patients [20]. As a result, the test for the JAK2 mutation was added to the 2008 World Health Organization criteria for the diagnosis of PV [21,22,23]. However, JAK2-negative PV cases have also been reported [22,23,24,25,26]. Therefore, the diagnosis of PV still requires comprehensive examination and consideration in clinical practice.
In consideration of the present case and the factors mentioned above, some measures can be adopted during the diagnosis of erythrocytosis or erythrocytosis combined with cancer. First, imaging examinations, such as ultrasound or computed tomography, should be performed, especially for patients with signs such as abdominal distention or splenomegaly to exclude secondary erythrocytosis. Additionally, patients with erythrocytosis for whom secondary factors have already been ruled out should be tested for the JAK2 mutation if possible to confirm the PV diagnosis.
RAE was initially developed in the 1970s [27]. It was performed to treat renal cancer and has been demonstrated to be a safe and effective technique with several decades of experience [28]. However, whether preoperative RAE is indeed beneficial for survival is still controversial [16, 28,29,30]. From our perspective, in the present case, preoperative RAE reduced the tumor blood supply, helped earlier ligation of the vessel, shortened the operation time, and played a positive role without any adverse effects. However, just one case is not yet illustrative of its benefit; further studies are needed to evaluate the advantages and disadvantages of preoperative RAE.
Certainly, this report still has limitations. For instance, erythrocytosis caused by EPO production was found in this case. The mechanisms of EPO production were not explored in this report and still require further research. The patient’s follow-up time was just 18 months. A longer follow-up is also needed to assess the patient’s prognosis and occurrence of relapse.
