PSMA-Guided Surgery Meets Immune Mapping in Node-Positive Prostate Cancer
TACTIC-P is designed around a rare pairing: intraoperative precision surgery and deep immune phenotyping in the same cohort. The single-center study will enroll 12 men with biopsy-proven prostate cancer and pelvic lymph-node uptake on preoperative PSMA PET, but without bone or visceral metastases. Every participant will undergo the same pathway, starting with intravenous gallium-68 PSMA-11, followed by PET/CT and then PSMA-radioguided surgery with a drop-in gamma probe. The operative plan combines excision of PSMA-positive lesions with extended pelvic lymph-node dissection and Retzius-sparing robot-assisted radical prostatectomy.
The scientific center of gravity is not just surgical localization. Investigators want to identify functional pathogen-specific bystander tissue-resident T cells inside the primary tumor and/or metastatic lymph nodes, then determine whether those cells can be quantitatively characterized well enough to support future personalized immunotherapy strategies. In plain clinical terms, the study is asking whether immune cells already living inside the cancer microenvironment carry a stable, measurable signature that can be linked to tissue residency, clonality, and functional responsiveness.
Intraoperative Localization and Tissue Harvesting in a Single Workflow
The study uses a tightly choreographed surgical sequence. On Day 0, participants receive the tracer at a dose described as approximately 1.8–2.8 MBq/kg, with a standard activity of about 160 MBq, and PET/CT follows roughly 60 minutes later. Surgery is then performed 4 to 8 hours after injection. During the operation, a positive lesion is defined by a count rate at least twice the background reference, allowing the surgeon to identify PSMA-avid targets in real time.
Fresh primary tumor tissue, metastatic lymph-node tissue, formalin-fixed paraffin-embedded samples, and matched peripheral blood are all collected. This matters because the study is not relying on a single assay or a single specimen type to build its biological case. It is instead linking operative findings with single-cell, spatial, and functional immune readouts so that tissue localization, phenotype, and function can be interpreted together.
The first six participants serve a practical purpose before any broader expansion of the platform. Those cases are intended to optimize tissue acquisition and molecular workflows. The next six participants extend the patient-derived tumor fragment platform and ex vivo immunologic testing, which gives the study a staged internal development plan rather than a one-shot sampling approach.
Defining Bystander T Cells by Tissue Residency, Clonality, and Function
The primary outcome is unusually specific. Investigators will measure the proportion of evaluable participants in whom functional pathogen-specific bystander tissue-resident T-cell populations or clonotypes are identified in the primary prostate tumor and/or matched metastatic lymph-node tissue. The prespecified definition draws on several layers of evidence: detection by scRNA-seq, scCITE-seq, and scTCR-seq; a tissue-resident or non-naive phenotype with markers such as CD69, 4-1BB/CD137, CD103, and/or CD49a; ex vivo activation or proliferation after stimulation with common viral peptide pools such as CMV, EBV, and influenza; and TCR clonotype identification that can be integrated with the single-cell and spatial datasets.
This is a demanding endpoint, and intentionally so. A cell population has to meet both phenotypic and functional criteria before it counts as a relevant bystander resident T-cell population. The design is trying to avoid overcalling immune presence on the basis of surface markers alone.
A single positive marker will not be enough here.
That bar is important because tissue-resident T cells in cancer can be biologically intriguing without being straightforwardly interpretable. A resident phenotype suggests local persistence, but the added stimulation assays are what may reveal whether these cells remain responsive to pathogen-derived antigens rather than merely sitting in the tissue in an exhausted or inert state. If the cells respond to viral peptide pools, the study may be able to map an immune memory layer that is present inside tumor-bearing tissue but not necessarily directed at the tumor itself.
Why the Study Could Matter for Node-Positive Disease Biology
The protocol is built around a central translational question in node-positive prostate cancer: whether immune activity in the tumor and draining nodal basin can be profiled in a way that informs recurrence prevention or personalized immunotherapy. The study’s title makes that aim explicit, but the practical value lies in the tissue combination. Metastatic lymph nodes, primary prostate tumor, and matched blood can each tell a different part of the story, and the integrated profiling strategy is meant to connect them.
The study also includes spatial profiling, cytokine and chemokine assays, bulk TCR sequencing, and functional stimulation with common viral peptide pools. Those assays are not decorative. They are the methods most likely to distinguish a bystander resident T-cell population from a tumor-reactive population or a circulating contaminant. The study’s hypothesis is that resident immune cells inside the primary lesion or nodal metastasis may be relevant to immune history, tissue persistence, and future therapeutic targeting.
Safety Follow-Up and the Limits of a Twelve-Patient Design
Participants are followed at Day 28 and Day 84 for laboratory tests, adverse events, perioperative outcomes, pathology, and postoperative data. The study also evaluates whether PSMA-radioguided surgery can detect pathologically positive lymph nodes and tracks perioperative safety through 12 weeks after surgery. Those are clinically meaningful observations, but the study is not built to establish efficacy in the usual confirmatory sense.
The investigators state plainly that this is a hypothesis-generating project and that it is not powered for confirmatory clinical testing. Enrollment is estimated at 12, the design is single-arm, and every participant receives the same treatment sequence. As a result, the study can generate mechanistic insight and feasibility data, but it cannot settle whether the immune findings predict recurrence, treatment response, or long-term outcome.
Even so, the work may still matter for a difficult subset of disease. Men with PSMA-positive pelvic nodes represent a clinically important group, especially when imaging suggests nodal spread but not distant metastasis. If the assay pipeline succeeds, the trial could establish a reproducible way to collect operative tissue and interrogate the immune compartment with enough depth to support later interventional studies.
The main unresolved issue is whether the immune signatures captured in these 12 men will prove consistent enough to shape a broader biomarker strategy. For now, the study is focused on feasibility, tissue quality, and biological signal rather than clinical endpoints, and its most concrete output will be whether the planned molecular workflow can reliably identify those pathogen-specific tissue-resident T-cell populations in nodal-positive prostate cancer.