Differential features between in situ and partial involvement by follicular and mantle cell lymphoma
| In situ FL/intrafollicular neoplasia* |
| Preserved general architecture |
| Centrocytes strongly positive for BCL2 and CD10 within GC |
| BCL-2 staining in centrocytes usually stronger than in mantle cells or reactive T cells |
| Involved follicles usually scattered, not confluent |
| GCs normal in size and often not completely replaced by BCL-2+ cells |
| Partial involvement by FL |
| Partial effacement of the architecture |
| Affected follicles usually restricted to a limited region of the lymph node |
| Tumor cells may be present in interfollicular areas |
| GCs expanded in size and completely replaced by tumor cells |
| In situ MCL* |
| Preserved general architecture |
| Mantle zones usually not expanded |
| Cyclin D1+ cells restricted to the mantle zones of reactive follicles with only scattered positive cells in interfollicular areas |
| Cyclin D1+ cells tend to accumulate in the inner layers of the mantle zone; not all mantle cells are positive |
| Mantle zone pattern in MCL |
| Architecture preserved or focally effaced |
| Mantle zones usually expanded |
| Cyclin D1+ cells replace virtually all the mantle zone of reactive follicles |
| Focal extension of clusters of tumor cells into interfollicular areas may be seen |
| In situ FL/intrafollicular neoplasia* |
| Preserved general architecture |
| Centrocytes strongly positive for BCL2 and CD10 within GC |
| BCL-2 staining in centrocytes usually stronger than in mantle cells or reactive T cells |
| Involved follicles usually scattered, not confluent |
| GCs normal in size and often not completely replaced by BCL-2+ cells |
| Partial involvement by FL |
| Partial effacement of the architecture |
| Affected follicles usually restricted to a limited region of the lymph node |
| Tumor cells may be present in interfollicular areas |
| GCs expanded in size and completely replaced by tumor cells |
| In situ MCL* |
| Preserved general architecture |
| Mantle zones usually not expanded |
| Cyclin D1+ cells restricted to the mantle zones of reactive follicles with only scattered positive cells in interfollicular areas |
| Cyclin D1+ cells tend to accumulate in the inner layers of the mantle zone; not all mantle cells are positive |
| Mantle zone pattern in MCL |
| Architecture preserved or focally effaced |
| Mantle zones usually expanded |
| Cyclin D1+ cells replace virtually all the mantle zone of reactive follicles |
| Focal extension of clusters of tumor cells into interfollicular areas may be seen |
FL indicates follicular lymphoma; MCL, mantle cell lymphoma; and GC, germinal center.
The terms “FL-like B cells” or “MCL-like B cell of uncertain significance” are recommended as alternatives to “FL in situ” and “MCL in situ” for clinical use in the future.