I. To perform pharmacokinetic studies on patients receiving fenretinide. (Phase I) II. To determine the intratumoral concentrations of fenretinide. (Phase I) III. To evaluate the in vivo mechanism of action of fenretinide. (Phase I) IV. To identify the predictors of response to fenretinide. (Phase I) V. To estimate the response rates, positron emission tomography (PET) response, overall survival (OS), progression-free survival (PFS), time to progression (TTP), and disease-free survival (DFS) of patients treated on this study. (Phase I) VI. To estimate the overall survival (OS), progression-free survival (PFS), time to progression (TTP), disease-free survival (DFS), and PET responses of patients treated on this study. (Phase II) VII. To perform pharmacokinetic studies on patients receiving fenretinide. (Phase II) VIII. To determine the intratumoral concentration of fenretinide. (Phase II) IX. To identify the predictors of response to fenretinide and fenretinide + rituximab in B-NHL. (Phase II) X. To evaluate the in vivo mechanism of action of fenretinide in B-NHL. (Phase II)