AbstractBackground and AimStereomicroscopic on‐site evaluation (SOSE) is a rapid evaluation method for endoscopic ultrasound‐guided tissue acquisition (EUS‐TA) with a high diagnostic sensitivity when the stereomicroscopically visible white core (SVWC) cut‐off value (≥ 11 mm) is met. We prospectively examined the association between SVWCs and the adequacy of tissue specimens, assuming subsequent comprehensive genome profiling (CGP).MethodsThis study included 66 consecutive patients with suspected unresectable pancreatic cancer who underwent EUS‐TA. The primary endpoint was the frequency of combined samples with ≥ 20% tumor cell content that met over twice the SVWC (T‐SVWC) cut‐off value, achieved through multiple punctures. The secondary endpoints were the number of punctures, the percentage of SVWC cut‐off values, adverse events, the positive diagnosis rate, and the tissue section area.ResultsThe median number of EUS‐TA punctures for suspected unresectable pancreatic cancer was 3 (range, 3–4); SVWC and T‐SVWC cut‐off values were obtained in 171/206 specimens and 65/66 patients, respectively. There were no EUS‐TA‐related adverse events. The positive diagnosis rate of EUS‐TA was 95.5%. Among the 63 patients meeting the T‐SVWC cut‐off value in pathological diagnoses, the median tumor cell content was 40% (range, 5–80%), with 57 patients having tumor cell content ≥ 20%. The median tissue section area was 15 (range, 3–40) mm².ConclusionsWhen performing EUS‐TA for unresectable pancreatic cancer with the intention of subsequent CGP, obtaining a high tumor cell content (≥ 20%) by assessing the T‐SVWC cut‐off value via SOSE may serve as a novel indicator for on‐site estimation of CGP suitability for EUS‐TA specimens.