Prognostic relevance of light chain 3 (LC3A) autophagy patterns in colorectal adenocarcinomas

The microtubule-associated protein 1 light chain 3 (LC3A) is an essential component of the autophagic vacuoles, forming a reliable marker of autophagic activity. In a previous study, the authors showed that LC3A immunohistochemistry renders three patterns of autophagic expression in breast carcinomas: diffuse cytoplasmic, perinuclear and 'stone-like' intracellular structures (SLS), each with a distinct prognostic relevance.

Tumour tissues from 155 patients with stage IIA-III colorectal adenocarcinomas, treated with surgery alone, were assessed immunohistochemically for LC3A. Median values were used as cut-off points to separate groups into low and high autophagic activity. Associations with prognosis and with lactate dehydrogenase-5 (LDH5) were sought.

High SLS counts were associated with metastases and poor prognosis, while the prominence of the perinuclear pattern was linked to localised disease and good prognosis. The cytoplasmic pattern was irrelevant. Furthermore, patients with increased SLS numbers, but suppressed perinuclear expression, were associated with LDH5 overexpression and had an extremely poor prognosis (3-year survival 16.5%). The prognosis improved considerably when high SLS counts were accompanied by intense perinuclear expression (3-year survival 67%) and were optimal when SLS numbers dropped below median values, irrespective of perinuclear status (3-year survival 94-100%). Multivariate analysis showed that SLS and perinuclear patterns were independent predictors of death events.

Perinuclear LC3A accumulation in colorectal tumour cells is a marker of good prognosis, presumably reflecting a basal autophagic activity. An abnormal or excessive autophagic response, as indicated by increased numbers of SLS, is linked to metastasis and poor prognosis.