A 73-year-old patient has been suffering from chronic atrophic gastritis for over 10 years. Objectively, her skin and mucosa are pale and subicteric, the tongue is bright red, with marked atrophy. The patient is hemodynamically stable. Sensitivity is symmetrically reduced in the patient's legs. Complete blood count: erythrocytes 1.5-1012/L, hemoglobin 60 g/L, color index -1.2, platelets 120-109/L, leukocytes 3.0-109/L, megalocytes, hypersegmentation of neutrophil nuclei. What complication of chronic atrophic gastritis has occurred in the patient?