A Diagnostic Revelation: Case of a Mucinous Carcinoma of the Breast

Abstract

Mucinous or colloid cancers are a rare subtype of invasive ductal carcinoma, making up only 2–3% of infiltrating carcinomas. Prevalence of pure mucinous breast cancer(PMBC) among infiltrating duct carcinomas in less than 60 year olds is 2–7%, and in less than 35 year olds, it is 1%. Mucinous carcinoma of the breast is divided into 2 subtypes, the pure type and mixed type. PMBC is characterized by a lower incidence of nodal involvement, favourable histological grade, and higher ER/PR expression. Axillary metastases are rare, though found in 12–14%. It has a better prognosis than infiltrative ductal cancer with 10-year survival being more than 90%. Here is the case of a 70-year-old female who presented with lump in the left breast since 3 years. On examination, we detected a left breast lump occupying the whole breast except lower outer quadrant, measuring 10 × 8 cm with overlying skin stretched with puckering and engorged veins seen, nipple displaced laterally and higher by 1 cm, firm to hard in consistency, and mobile with breast tissue. Sonomammography, mammography, FNAC and biopsy were suggestive of benign phyllodes tumour. Patient was hence posted for simple mastectomy on the left side with removal of attached lymph nodes (near axillary tail). Histopathological examination revealed pure mucinous breast carcinoma with nine lymph nodes, free from tumour and showing reactive hyperplasia. Immunohistochemistry studies demonstrated ER + , PR + , HER-2-NEU-. The patient was started on hormonal therapy. Therefore, mucinous carcinoma of the breast is a rare entity with imaging features sometimes mimicking a benign tumour such as Phyllodes tumour, hence making it important to include it as a differential diagnosis in our daily practice. It is especially important in the subtyping of carcinoma of the breast since it carries a favourable risk profile with less chances of lymph node involvement, higher hormone receptor positivity and good response to endocrine treatment.

Introduction

Breast cancer remains the most frequent cancer in women and the second most frequent cause of cancer deaths [1]. Worldwide, it is the most frequently diagnosed cancer accounting for 23% of total cancer cases and 14% of cancer deaths [1].

Breast cancer has ranked as the number one cancer among Indian females with age-adjusted rate as high as 25.8 per 100,000 women and mortality 12.7 per 100,000 women. Mucinous or colloid cancers are a rare subtype of invasive ductal carcinoma, which constitute only 2–3% of infiltrating carcinomas [2, 3]. The reported prevalence of pure mucinous breast cancer among infiltrating duct carcinomas in the 6th decade onwards is 2 to 7%, and in less than 35 year olds, it is 1% [4]. Mucinous carcinoma has a more favourable prognosis than invasive carcinoma of no special type or invasive lobular carcinoma [4].

Clinical Presentation

A 70-year-old female presented with lump in the left breast since 3 years, insidious onset, slow growing associated with pain which has been increasing in the last 3 months, and associated with unquantified weight loss. On examination, she had moderate build, was well-nourished with normal facies, gait and attitude. On general physical examination, vitals were found to be stable.

On Local Examination

The right breast was normal. Left breast was enlarged with lump occupying the whole breast except lower outer quadrant, approximately measuring 8 × 7 cm in size, with an irregular surface, overlying skin stretched and pigmented. Puckering and engorged veins were also seen. The left nipple was displaced laterally and higher by 1 cm. The lump was firm to hard with tenderness and irregular margins. It was freely mobile within the breast tissue without fixity to the skin (Fig. 1).

Fig. 1.

Clinical picture of the left breast demonstrating a lump of size 8 × 7 cm, occupying almost all quadrants except lower outer, with overlying stretched, pigmented skin with engorged veins and outward displacement of the nipple. Preoperative marking for flap has been shown

The areola was normal with no local rise of temperature. No nipple retraction/discharge was noted. The lump was not fixed to the pectoralis muscle or to the chest wall. No axillary or supraclavicular lymphadenopathy was noted bilaterally, and no other lumps were found.

Based on the above findings, the provisional diagnosis of left-sided phyllodes tumour was deduced.

Investigations

We first proceeded with a sonomammogram of the left breast which showed a diffuse, heteroechoic solid mass involving the entire left breast with areas of necrosis and internal vascularity. No axillary nodes were found (Fig. 2). Mammogram demonstrated a well-circumscribed lobular opacity with regular borders suggestive of phyllodes tumour (Fig. 3). Fine needle aspiration biopsy (FNAC) was performed which was suggestive of benign phyllodes tumour with absence of atypia. The Trucut biopsy report from an outside hospital demonstrated the presence of a phyllodes tumour with stromal hypercellularity. The chest x-ray and ultrasound abdomen and pelvis were essentially normal.

Fig. 2.

A Sonomammogram of the left breast demonstrating the solid, heteroechoeic lump occupying almost whole of the breast, with necrosis and central vascularity. b Sonomammogram of left breast demonstrating the heteroechogenicity of the mass. No axillary nodes noted

Fig. 3.

Mammogram of the left breast a craniocaudal view and b mediolateral oblique view demonstrating a lobular opacity with regular borders suggestive of phyllodes tumour

Operative Findings

Patient underwent simple mastectomy under general anaesthesia, on the left side. Intraoperatively level I lymph nodes, closely attached to the axillary tail, were detected which prompted us to go ahead with level I axillary L.N dissection. Intraoperatively, the lump was hard, measuring approximately 10 × 8 cm. It was well circumscribed with gelatinous cut surface, necrosis and grated-feel on cutting (Fig. 4).

Fig. 4.

Intraop findings—simple mastectomy with incidental level I LN’s dissection also done. Flaps being raised are shown

Histopathology Report

On gross examination of the left-sided simple mastectomy specimen, the cut surface showed ill-defined tumor mass measuring 7 × 6 × 5 cm with gelatinous material and necrosis (Fig. 5). On microscopic examination, the section showed the presence of a malignant neoplasm in solid sheets, cribriform, micropapillary pattern and small clusters of tumor cells in pools of extracellular mucin (> 90%). The tumor cells were small, round with hyperchromatic nuclei, prominent nucleoli and 2–3 mitoses/hpf. The intervening stroma showed acute inflammatory exudate, haemorrhage and extensive necrosis. Lymph nodes were nine in number, free from tumour and showed reactive hyperplasia. Histologic type was revealed to be pure mucinous breast carcinoma (Fig. 6). Immunohistochemistry showed nuclear positivity for oestrogen receptor and progesterone receptor and negative for cell membrane Her-2-neu receptor.

Fig. 5.

Gross specimen: Ill-defined tumour mass measuring approx. 7 × 6 × 5 cm, with gelatinous surface and areas of necrosis

Fig. 6.

Microscopy with H&E staining (40 ×): shows malignant growth in small clusters of tumor cells in pools of extracellular mucin. Intervening stroma shows haemorrhage and necrosis (H&E: haematoxylin and eosin staining)

The oestrogen receptor proportion score was 4 (34–66% cell’s nuclei stain positive for ER receptor) and intensity score was 3 (strong intensity) bringing the total Allred score (proportion score + intensity score) to 7.

The progesterone receptor proportion score was also 4 (34–66% cell’s nuclei stain positive for PR receptor) and intensity score was 3 (strong intensity) bringing the total Allred score (proportion score + intensity score) to 7, same as the oestrogen receptor score (Fig. 7). It was negative for Her-2-Neu receptor.

Fig. 7.

IHC staining under 20 × : (1) ER positivity, (2) PR positivity, (3) Her-2-Neu negativity

Follow Up

The patient came for suture removal on post operative day 10. On seeing her HPE report, hormonal therapy was instituted — anastrozole-1 mg O.D for 5 years and was asked to review in a month. She did not however return and was therefore lost to follow-up in spite of repeated attempts to contact her.

Discussion

PMBC (pure mucinous breast carcinoma) is an uncommon type of carcinoma with a prevalence of 1–5% of all breast cancers and usually occurs in patients aged 75 years or older [5, 6]. This entity is a slow-growing tumour, with an estimated growth rate of one-third compared to invasive ductal carcinoma. It is divided into 2 subtypes, the pure type and mixed type. The distinction between the 2 subtypes is based upon the quantification of cellularity. The pure type consists exclusively of tumor tissue with extracellular mucin production in over 90% of the tumor, while the mixed form also contains an infiltrating ductal epithelial component with mucin (known as invasive ductal carcinoma with mucinous degeneration) [7].

Pure mucinous breast cancer (PMBC) is characterized by a lower incidence of nodal involvement, favourable histological grade and higher oestrogen receptor (ER) and progesterone receptor (PR) expression. In fact, PMBC patients generally have a more favourable prognosis compared to invasive ductal carcinoma patients, with a low recurrence rate [6]. It is the extracellular mucin rather than the tumor cells that invade the stroma which explains the good prognosis of pure mucinous carcinoma [8].

Axillary metastases are rare, though generally found in 12–14% in most series studies [6]. However, axillary staging by sentinel lymph node biopsy and the administration of adjuvant RT and endocrine therapy after breast-conservation therapy for mucinous cancer were common [9]. Paramo et al. reported that axillary lymph node staging in these patients might not be necessary because PMBC appears unlikely to metastasize [10]. Unusual complications include pseudomyxoma peritonei and mucinous embolism [4]. Gorantla et al. in 2015 reported a case of mucinous carcinoma mimicking as a phyllodes tumour hence making it important as in our case as well, to include it as a differential diagnosis [11]. Iqbal BM et al. in 2016 reported a case of mucinous breast carcinoma in a 30-year-old female.

Ultimately, we have confirmed that PMBC is associated with outstanding overall and disease-free survival in literature [5, 12].

Conclusion

Pure mucinous carcinoma of the breast is a rare tumour accounting for 1–5% of breast tumours, characterized by imaging features of a benign mass and having a better prognosis than infiltrating ductal cancer. In our case, we made a provisional clinical diagnosis of a phyllodes tumour which turned out later to be a case of mucinous breast carcinoma. Clinically, mucinous carcinoma manifests as a palpable lump, with a mammographic appearance of well-defined and lobulated lesion thus being mistaken for a benign mass. Axillary metastases are rare, even more so when the tumour diameter is less than 1 cm. The prognosis rate is better for pure mucinous carcinoma as they have indolent growth, less incidence of metastasis and hormone receptor positivity with good response to treatment.

Data Availability

Taken with due consent from patient.

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Competing Interests

The authors declare no competing interests.