Does(1) lesion
location/extent or (2) amount of tumor correlate with BCR rate for
prostate-confined cancer?
There appears to be consensus about
(1): no, it doesn't. The 8th edition of the TNM Staging Guide did away with the a, b, c subdivision of the pT2 pathological stage. I've seen two or three studies subsequent to this change that have confirmed the reasonableness of this decision. It appears that how extensively your PCa was distributed throughout your prostate does not affect your chances of BCR. My 2017 report has me as pT2c (bilateral involvement). Not long after, Forum brothers began listing recent path stagings without any letters as path labs switched from the 7th to the 8th edition.
What about
tumor burden? This may be listed as "quantitation" in a path report, or something like "percentage of prostate involved by tumor". Does this predict BCR? I was under the impression that past studies were divided about
the answer, but had leaned toward a "yes" answer. If I'm remembering correctly, one study concluded that 17% and below involvement was favorable, although I don't remember any associated stats.
Today I came across this study from MSK:
In Organ-confined Prostate Cancer, Tumor Quantitation Not Found to Aid in Prediction of Biochemical Recurrence (2020)
"In the eighth edition AJCC staging, all organ-confined disease is assigned pathologic stage T2, without subclassification.
We investigated whether total tumor volume (TTV) and/or maximum tumor diameter (MTD) of the index lesion are useful in improving prediction of biochemical recurrence (BCR) in pT2 patients. We identified 1657 patients with digital tumor maps and quantification of TTV/MTD who had pT2 disease on radical prostatectomy (RP). Multivariable Cox regression models were used to assess whether TTV and/or MTD are independent predictors of BCR
when adjusting for a base model incorporating age, preoperative prostate-specific antigen, RP grade group, and surgical margin status. If either tumor quantification added significantly, we calculated and reported the c-index. Ninety-five patients experienced BCR after RP; median follow-up for patients without BCR was 5.7 years. The c-index was 0.737 for the base model. Although there was some evidence of an association between TTV and BCR (P=0.088), this did not meet conventional levels of statistical significance and only provided a limited increase in discrimination (0.743; c-index improvement: 0.006). MTD was not associated with BCR (P>0.9). In analyses excluding patients with grade group 1 on biopsy who would be less likely to undergo RP in contemporary practice (622 patients; 59 with BCR), TTV/MTD was not a statistically significant predictor (P=0.4 and 0.8, respectively).
Without evidence that tumor quantitation, in the form of either TTV or MTD of the index lesion, is useful for the prediction of BCR in pT2 prostate cancer, we cannot recommend its routine reporting."
[Emphasis mine. Remember also that pT2 includes men with a positive surgical margin, for whom I assume this discussion does not apply.]
You might think that, OK, the cancer was confined, but wouldn't a larger index lesion or total amount of tumor indicate that the PCa has been around longer, and has therefore had more time to send out tumor cells that can metastasize? My reading of studies, including genomics, is -- not really. Many men already have circulating tumor cells (CTC) before treatment -- however, in the majority of cases, these cells simply cannot establish themselves outside the prostate. Or, if you are high genomic risk for mets, micromets may have been established long before the cancer in the prostate has grown to its size at RP. Either way, tumor burden itself may not be an indicator of BCR risk -- again, we are talking about
prostate-confined PCa at the time of treatment. As far as genomics, I've mentioned before that Decipher studies have shown that low, intermediate, and high risk for metastasis cuts across
all Gleason grades, from 6 to 10. For example, I was fortunate (so far) in the my Decipher score on my G9 tissue came back low risk. A study showed that about
10% of men with
pT2, post-op confirmed G6 have/had cancer with a tendency to form higher-grade lesions that are a high-risk for mets.
So while it seems logical to look at (a) how widespread one's cancer is in the prostate, (b) how much there is in total, or (c) the size of the largest lesion, research on (b) and (c) is saying "not so fast." However I'm sure the above study won't be the last word on this.
Food for thought.
Djin