**5. Pathology**

**Figure 4.** Scenery of GasLESS via a coin-sized port using the 3D-HMD system.

**Figure 5.** Pathology of ACD-associated RCC in a 65-year-old man. a: Macrophotograph. b: Microphotograph. The tu‐

a b

Figure 5

150 Updates in Hemodialysis

mor tissue contains oxalate crystals.

Many investigators had considered for a long time that clear cell or papillary RCC is a common histological type of renal cancer arising from ACDK [15, 16]. However, a new disease entity of ACD-associated RCC showing characteristic histologic features has been established.

#### **5. 1. Characteristics of Histological Types**

Papillary RCC was previously reported to be the most common histological subtype found in ACDK in dialysis patients, accounting for 42-71% of cases [15, 17, 71]. Since the establishment of the current histological classification, ACD–associated RCC is the most common histological type of RCC occurring in ESRD kidneys [19]. ACD-associated RCC was found in 36% of surgically resected ESRD kidneys [10]. Some investigators reported that histological patterns of RCC change according to the duration of dialysis. ACD-associated RCC was the major histological subtype in those on dialysis for 10 years or longer [26, 72].

Clearcell(tubulo)papillaryRCCwasalsoinitiallyreportedinpatientswithESRD[10].However, the majority of cases reported subsequently were not associated with ACDK [73-76]. Reported‐ ly, clear cell papillary RCC comprises less than a few percent of all RCCs [75, 77].

#### *5. 1. 1. ACD-associated RCC*

Diagnostic criteria for ACD include the presence of cystic structures occupying at least 25% of the renal parenchyma or greaterthan three cysts per kidney [78]. ACD-associatedRCC appears as a nodule arising from cystic wall, occasionally completely filling the cyst, or as a solid mass separate fromthe cyst(Fig. 5a).Non-cystic tumorsarewell circumscribedandmaybe surround‐ ed by a thick fibrous capsule showing dystrophic calcification. The cut surface of the tumor varies from grey tan to yellowish or brownish and hemorrhage or necrosis is occasionally seen [25]. Multifocality and bilaterality are seen in >50% and >20% of the cases, respectively [10].

Microscopically, ACD-associated RCC is defined as a tumor having eosinophilic or oncocytic cytoplasm and is frequently associated with intratumoral oxalate crystal deposition [10, 17, 79] (Fig. 5b). Some investigators suggest that many microcysts maybe formed by intracyto‐ palsmic vacuoles mainly due to degenerative change. These crystals are multicolored under polarized microscopic observation. Papillary, tubular, cribriform or solid growth pattern may also be seen. Nuclear grade is frequently classified as Fuhrman grade 3 [10, 17, 25]. Clear cell change, sarcomatoid change or rhabdoid features may be present in some cases [10, 80, 81]. Immunohistochemically, neoplastic cells of ACD-associated RCC are positive for α-methyl‐ acyl-coenzyme A racemase (AMACR), CD10, CD57, GST-α, vinculin and c-met, but negative for cytokeratin 7 (CK7) and high molecular weight cytokeratins [10, 25, 27, 81-83].

#### *5. 1. 2. Clear Cell Papillary RCC*

Clear cell papillary RCC is seen in ESRD patients without ACDK. The tumors appear well circumscribed and usually well encapsulated. The cut surface is tan-white to yellow with grossly apparent fibrotic areas and ranges from completely solid to predominantly cystic.

Microscopically, clear cell papillary RCC have variable tubular/acinar, papillary, and cycti‐ carchitectures [10, 74, 75]. The tumor cells have clear cytoplasm. Nuclear grade is often classified into Fuhrman grade 1 or 2. In contrast to ACD-associated RCC, clear cell papillary RCC is positive for CK7 but negative for AMACR and CD10 [74, 75].
