Background: Currently, granular-type laterally spreading tumors (LST-G) have been classified into uniform [LST-G (UNI)] and nodular mixed [LST-G (MIX)] subtypes. However, the progression pattern of each subtype has not been evaluated in detail. The present study was designed to assign adequate treatment strategies to each LST-G subtype, based on the progression pattern.
Methods: This retrospective study included 457 consecutive patients with 482 LST-Gs that had been removed endoscopically or surgically in a tertiary cancer center between September 2002 and December 2011. We classified the tumors as LST-G (UNI) or LST-G (MIX) subtypes. We analyzed clinicopathological characteristics and submucosal invasion rates for both subtypes, and we determined the incidence of submucosal invasions associated with the largest nodules for each subtype.
Results: We evaluated the histopathological data from 136 LST-G (UNI) and 316 LST-G (MIX) lesions with diameters of 10-19 mm (14%), 20-29 mm (26%), 30-39 mm (25%), or >40 mm (35%). Submucosal invasions were observed in 3 (1.8%) LST-G (UNI) and 49 (15.5%) LST-G (MIX) lesions. In LST-G (MIX) lesions, the submucosal invasion incidences (within a tumor-size category) were as follows: 5.8% (10-19 mm), 11.1% (20-29 mm), 14.7% (30-39 mm), and 19.1% (>40 mm), respectively. In LST-G (MIX) lesions that showed submucosal invasions, the invasive cancers were located under the largest nodule (69%; 34/49), outside the largest nodule (25%; 12/49), or in both sites (6%; 3/49).
Conclusions: Our results indicated that, for LST-G (UNI) lesions, piecemeal resections would be acceptable due to the low risk of submucosal invasion. For LST-G (MIX) lesions, particularly those with diameters ≥20 mm, en bloc removal in an endoscopic resection is preferable for sufficient histological evaluation.