Anisometric Cell Lipoma: A Predominantly Subcutaneous Fatty Tumor With Notable Variation in Fat Cell Size But Not More Than Slight Nuclear Enlargement and Atypia

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Abstract

Having repeatedly encountered at least predominantly subcutaneous lipomatous tumors displaying significant variation in fat cell size but only equivocal to slight nuclear atypia among consultation cases and having been unsure about their appropriate classification and their behavior, I decided to carry out a review. To this end, consultation cases in our files that were originally submitted before 2008 and were described in their reports as showing these features were retrieved. Criteria for including a case in the study were that there be adequate histological material that indeed demonstrated the characteristics stated above and that there be at least some follow-up information. The study group as thus selected was composed of 13 patients: 12 men and 1 woman aged 36 to 79 years (median, 57 years). The most common tumor locations were the neck and back (3 each; 1 man had 2 separate tumors involving the neck and back). Other sites included the chest wall (n = 2), breast (n = 1 [the woman]), breast and axilla (n = 1 [a man]), arm (n = 1), shoulder (n = 1), scrotum (n = 1), and pubic area (n = 1). All the tumors were subcutaneous. Excision (sometimes in fragments) was the initial treatment in all cases. This was followed by re-excision in 3 cases (shoulder, breast, and scrotum, including hemiscrotectomy and orchiectomy for the scrotal example), with all re-excisions being negative for tumor. When known, tumor size (which was estimated from aggregate or largest fragment dimensions in the instances of fragmented specimens) ranged from 4.1 to 9.1 cm (median, 6 cm). Histologically, all the tumors demonstrated variable fat cell size, sometimes strikingly so. In contrast to this, nuclear enlargement and atypia ranged from equivocal to slight. Microscopic (often single cell) foci of fat necrosis, which varied from occasional to plentiful, were a consistent finding. Some tumors had an intermingled fibrous or fibromyxoid component, but this never dominated and always lacked nuclear atypia (which was instead confined to fat cells). On follow-up of 4 to 11 years (median, 9 years), 10 patients had no recurrence of the tumor. Two had local recurrences excised, 1 at 6 years (neck) and 1 at 9 months (the patient with neck and back tumors, both of which recurred); additional follow-up could not be obtained on either patient. A third patient (breast and axilla) had a local recurrence that had not been excised at the latest follow-up of 9 years. Not included in the study group (because of lack of follow-up) but reported separately is the case of a 37-year-old man who had bilateral retinoblastomas as an infant, developed multiple lipomas as an adult, and recently had 2 lesions excised from the scrotal/inguinal area and the buttock, respectively, which both showed the features of the tumors in the study group. It was concluded that the tumors reported in this review form a category distinct from both atypical lipomatous tumors and ordinary lipomas by virtue of their combination of greatly preponderant occurrence in men, usual subcutaneous location, significant variability of fat cell size coupled with equivocal to minor nuclear atypia, and appreciable but relatively low rate of local recurrence. The name “anisometric cell lipoma” is suggested for them.

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