Mucinous tumours of the ovary

Abstract

Mucinous tumours of the ovary demonstrate marked morphological diversity, both within the group as a whole and in individual tumours. In this review, we focus on practical problems in interpretation and nomenclature. Recent developments of significance, including the recognition of Müllerian mucinous tumours and the distinction of expansile from destructive stromal invasion in carcinomas, are reviewed. Intriguing phenomena such as the occurrence of mural nodules that range from reactive proliferations to anaplastic carcinoma are discussed, as are other varied findings such as occasionally prominent mucin granulomas and rare primary tumours with focal signet ring cell morphology. The problematic area of metastatic mucinous neoplasia is considered. The gross and histological features of secondary mucinous neoplasia are reviewed, with specific comments regarding tumours arising from the appendix, which are associated with particular features when they spread to the ovary. The famous Krukenberg tumour is briefly discussed because of its definitional content of mucin-filled signet ring cells. Finally, the enigmatic occurrence of mucinous epithelial cells in a variety of ovarian tumours not traditionally considered ‘mucinous’ is noted. The latter include sex cord tumours, usually Sertoli-Leydig cell tumours but occasionally granulosa cell tumours, and entities as different as benign Brenner tumours and highly-malignant small cell carcinomas of hypercalcaemic type.

Introduction

Like many forms of ovarian neoplasia, mucinous tumours exhibit a remarkable clinicopathological spectrum. They are most often diagnosed in the fourth to sixth decades of life, but they can be seen at any age and are the most common surface epithelial tumour of children and adolescents. The category includes mucinous cystadenomas (Figure 1), which although benign can be huge and significantly symptomatic; borderline tumours of low malignant potential; and carcinomas that range in behaviour from relatively indolent to highly aggressive. A morphological continuum exists from mucinous cystadenoma to mucinous carcinoma, and epithelium that varies from benign to borderline to frankly malignant is frequently found within a single tumour. Because of this continuum, drawing the line between these three major categories of neoplasia can be problematic. Even within the carcinoma group itself, there is a great diversity of appearance and behaviour, which can be considered in three main categories:

• Tumours with expansile invasion and a good prognosis; with rare exceptions;

• Well- to moderately-differentiated tumours with destructive invasion and an associated drop-off in prognosis, but one which is still generally favourable when the tumours are stage I;

• High-grade adenocarcinomas, including some with an anaplastic component that, particularly when high-stage, can be rapidly fatal.

Another diagnostic challenge is presented by metastatic mucinous tumours from a variety of sites as they may be grossly indistinguishable from primary ovarian neoplasms. The overlap extends treacherously to microscopic evaluation, although well-sampled tumours will usually give clues to their true nature. The extent to which this is a common problem in ovarian tumor pathology interpretation has only been emphasized in the last decade or so.

In this review, we will focus on practical aspects of pathological evaluation and new information regarding mucinous tumours of the ovary. The emphasis will be on primary mucinous cystic neoplasms, but we will also discuss the diagnostic problems that metastatic mucinous carcinomas may pose. Other ovarian neoplasms that are not considered fundamentally mucinous but which can have mucinous cells of varying prominence will be briefly considered. The reader is referred to a number of excellent sources in the recent literature regarding ovarian mucinous tumours,1, 2, 3, 4, 5, 6 and as thorough literature reviews are available in those citations, our referencing herein will be selective. The original reports cited, and many others in the reference lists of those papers, provide detailed information on survival figures that will not be repeated here in a contribution intended to provide, with the aid of liberal use of illustrations, a guide to practical diagnostic issues. The role of immunohistochemistry in evaluating mucinous tumours has been much investigated in recent years and the reader is referred to reviews of that topic.7, 8, 9 From the viewpoint of daily practice, however, there are still relatively few firm aids provided by this technique. Traditional careful gross and routine microscopic evaluation, aided in some cases by due note of the clinical background, will yield the correct interpretation in the vast majority of cases.