Criteria for the cytologic subclassification of follicular lymphomas: A Proposed alternative method

Multiple clinicopathologic studies have demonstrated that the follicular or nodular lymphomas as a group have a favorable prognosis and that each histologic subtype of follicular lymphoma has a better survival than the corresponding diffuse lymphoma of similar cytologic composition (Jones et al., 1973; National Cancer Institute, 1982; Patchefsky et al., 1974). The follicular lymphomas are now viewed as an immunologically homeogeneous group of tumors derived from follicular B lymphocytes (Jaffe et al., 1974). Studies by Lukes and colleagues relating the cytology of the neoplastic cells to B lymphocytes found in normal germinal centers have carefully described the broad spectrum of cytologic differentiation which may be observed within these tumors, ranging from small cleaved lymphocytes to large transformed lymphoid cells of the cleaved and non-cleaved cell type (Lukes and Collins, 1974; Lukes et al., 1978). Most classifications (Table 1) divide these lymphomas into three subtypes based on the relative proportion of small and large lymphoid cells present within the neoplastic follicles [predominantly small cleaved cell (FSC), mixed small cleaved and large cell (FM), and predominantly large cell (FL)], however most of the criteria which have been proposed to make the distinctions between the individual cell types are not well defined, are often difficult to employ, and the means by which they are used vary from one observer to another (National Cancer Institute, 1982; Rappaport et al., 1956; Rappaport, 1966). Rappaport el al., originally proposed that the follicular lymphomas be divided into categories based on the cytologic composition of the neoplastic proliferation (Rappaport et al.. 1956). The distinction between the three subtypes listed in Table 1 was to be based on the relative proportion of neoplastic small lymphoid cells to larger cells which Rappaport regarded at the time as reticulum cells (Rappaport et al., 1956; Rappaport, 1966). These small and large cell populations were shown to correspond to the follicular B lymphocytes of the small cleaved and large cleaved and non-cleaved cell types later recognized by Lukes et al. (Lukes and Collins, 1974). In this scheme FSC would be composed predominantly of small cleaved lymphocytic cells with a scattering of larger cells. FM would be composed