- This study determined whether the presence of biopsy tract seeding with perinephric fat invasion (BTS-P) in renal cell carcinoma, in the absence of any other upstaging variable(s), should be considered a criterion for upstaging to pT3a
- Among 33 patients with perinephric fat invasion (PFI) on biopsy specimens, 10 had BTS-P as the only upstaging variable in otherwise pT1 tumors and 23 had true invasion (PFI alone, n=4; both PFI and BTS-P, n=2; or PFI with other forms of invasion, n=17)
- Cancer-specific survival was significantly better in patients with BTS-P alone than in those with true invasion (P=0.04)
- A meta-analysis of the cohort with 12 additional cases from the literature confirmed that cancer-specific survival was significantly better in patients with BTS-P than in patients with true invasion (P=0.02)
- BTS-P alone does not appear to be behave similarly to other forms of true invasion and should not be considered a criterion for upstaging to pT3a, but no definitive conclusion can be drawn from this small study
Advanced imaging has led to more frequent detection of incidental renal masses, which are benign in 20%–30% of cases. Percutaneous renal tumor biopsy is used increasingly often to evaluate these masses with the goal of avoiding unnecessary treatment.
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A potential complication, although infrequent, is biopsy tract seeding (BTS). One such scenario is that tumor cells are inadvertently misplaced into perinephric fat (BTS-P). More commonly, though, perinephric fat invasion (PFI) occurs as part of the pathologic cancer process.
When BTS-P is noted, the pathologist is faced with the dilemma on how to stage the tumor. The American Joint Committee on Cancer staging manual (eighth edition) recommends the pT3a category for tumors with PFI. However, the clinical significance of BTS-P is unknown.
Aida Valencia-Guerrero, MD, former Genitourinary Pathology fellow with the Department of Pathology at Massachusetts General Hospital, Kristine Cornejo, MD, a genitourinary pathologist at Mass General and the Mass General Cancer Center, and colleagues recently conducted the first study of this issue, finding patients with BTS-P have better survival than those with true invasion. They report the details in Histopathology.
The researchers determined that between 2005 to 2015 at Mass General, 304 patients underwent percutaneous renal tumor core biopsy before nephrectomy for renal cell carcinoma. Specimens from 33 patients showed PFI. The team compared two groups:
- In group 1, 10 patients had BTS-P as the only upstaging variable in otherwise pT1 tumors
- In group 2, 23 patients had true invasion: four had PFI alone, two had both PFI and BTS-P and 17 had PFI with sinus/hilar fat invasion (SFI) and/or renal vein invasion (RVI)
Researchers then compared survival between groups as follows.
BTS-P alone vs. true invasion:
- Cancer-specific survival (CSS)—worse with true invasion (P=0.04)
- Overall survival (OS)—no difference between groups
PFI ± BTS-P vs. PFI + SFI/RVI:
- CSS—worse with PFI + SFI/RVI (P=0.002)
- OS—worse with PFI + SRI/RVI (P=0.008)
PFI, BTS-P, or both vs. PFI + SFI/RVI:
- CSS—worse with PFI + SFI/RVI (P=0.0005)
- OS—worse with PFI + SRI/RVI (P=0.002)
Meta-analysis With Historical Cases
Because the cohort was small, the researchers combined it with 12 patients identified from a literature review. 21 of the 45 patients (47%) had otherwise pT1 tumors with BTS-P alone whereas 24 (53%) showed true invasion.
CSS and OS were significantly better in patients with PFI ± BTS-P than in those with PFI + SRI/RVI (P=0.02 and P=0.002, respectively).
BTS-P May Not Need To Be Upstaged to pT3a
Pathology departments should develop protocols that require thorough evaluation and sampling of grossly recognizable renal biopsy site changes, as this will increase the likelihood of identifying BTS-P. BTS alone does not appear to behave like other forms of true invasion and should not be upstaged to pT3a. However, no definitive conclusion about staging can be drawn from this small study.
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