Laterally spreading tumors

Laterally spreading tumors (LSTs) are a distinct category of colorectal lesions characterized by their nonpolypoid, flat appearance and their lateral growth pattern rather than vertical growth. These lesions are defined as being at least 1 cm in size and are considered precancerous or potentially cancerous. LSTs are important to identify and classify due to their unique growth behavior and varying risks of malignancy. They are generally detected during colonoscopy and are often more challenging to identify compared to polypoid lesions due to their flat morphology. Early detection and removal of LSTs are critical to prevent progression to colorectal cancer.

### Categories of LSTs:

LSTs are broadly divided into two main categories: granular (LST-G) and non-granular (LST-NG). These subtypes are differentiated based on their surface appearance and histological features, and each has distinct clinical implications.

1. **Granular (LST-G):**

LST-G lesions are characterized by a granular surface, often appearing as a collection of small nodules or granules. These lesions are more common and generally have a lower risk of malignant transformation, with approximately 10% containing cancer. LST-Gs are further subcategorized into homogeneous and nodular mixed types. Homogeneous LST-Gs have a uniform granular appearance, while nodular mixed types have areas of larger nodules. Although the overall risk of malignancy is low, larger lesions or those with mixed nodular patterns may carry a slightly higher risk.

2. **Non-Granular (LST-NG):**

LST-NG lesions have a smooth or flat surface without granularity. They are less common but are associated with a significantly higher risk of malignancy, with up to 33% of these lesions containing cancer. LST-NGs are further classified into flat-elevated and pseudo-depressed types. The pseudo-depressed subtype, in particular, is highly suspicious for malignancy and requires careful evaluation and management. Due to their higher cancer risk, LST-NG lesions are often prioritized for removal and histopathological examination.

### Clinical Significance:

The distinction between LST-G and LST-NG is essential for determining the appropriate management strategy. LST-G lesions, especially smaller ones, may be managed conservatively or with endoscopic resection, while LST-NG lesions often warrant more aggressive intervention due to their higher potential for malignancy. Advanced endoscopic techniques, such as endoscopic submucosal dissection (ESD) or endoscopic mucosal resection (EMR), are commonly used for the complete removal of these lesions. Regular surveillance and follow-up are also critical for preventing recurrence or progression to colorectal cancer.