In conclusion, the cases presented in this report support the use of a “wait and watch” strategy for MCL with no risk factors and indolent behavior, such as lack of B symptoms, normal lactate dehydrogenase (LDH) and β2 microglobulin (β2M) levels, a low MIPI score, a maximum tumor diameter of less than 3 cm, a low SUV on PET/CT (< 5), a Ki-67 value of < 30%, and non-blastoid cytology. This evidence concerns the gene B2M and mantle cell lymphoma.