Secondary thyroid malignancy from metastatic colon lymphoma

Abstract

Primary thyroid malignancy is more frequent than secondary. This case report describes a colon lymphoma with unique thyroid metastasis. When a thyroid lesion appears in an extension study such as Positron emission tomography–computed tomography marked with 18F-2-fluoro-2-deoxy-D-glucose, it is recommended to perform an ultrasound. The correct study with ultrasound and cytology obtained through fine needle aspiration on thyroid lesion allowed to refine the diagnosis and provide the correct treatment.

Background

Thyroid involvement secondary to a lymphoma of another location is an infrequent event, with a frequency of around 0.2%.¹

When a thyroid lesion appears on an imaging test such as Positron emission tomography–computed tomography (PET-CT) marked with 18F-2-fluoro-2-deoxy-d-glucose (18-F-FDG), normally used in the lymphoma extension study,² it is advisable to supplement the study with ultrasound, also assessing the need to perform fine needle aspiration (FNA) if the imaging test was suggestive of malignancy, since it is the first test to be performed given its good performance, despite not being exempt from limitations.³

Secondary thyroid lymphoma presents differences with respect to the primary lymphoma at the aetiological, pathophysiological and clinical–radiological levels. In the case of secondary thyroid lymphoma, there has been no evidence of positive autoimmunity, which is why, unlike primary lymphoma, Hashimoto’s thyroiditis is not a risk factor for its development. In addition, hypothyroidism is very rare.⁴

In the case shown below, a secondary thyroid lymphoma was found incidentally during the performance of a PET-CT marked with 18-F-FDG.

Case presentation

A 53-year-old man was seen in outpatient follow-up due to abdominal pain and a 6 kg weight loss in the last 2 months. Backgrounds of interest were an active hepatitis B infection without treatment and a cardiac ablation due to atrial fibrillation.

By this clinic, he went to the emergency room, where an abdominal ultrasound was performed where an ascending colon segment with very thickened walls and irregular morphology was evident, with discrete oedema of pericolic fat. Given these findings, it was decided to enter the Digestive Medicine service for study in the event of suspicion of colon neoplasia.

During the admission, a colonoscopy was requested, which showed a large excrescent and friable tumour at the ascending colon level. Biopsy samples were taken with the result: diffuse large B cell lymphoma with Bcl-6 (3q27) positive and C-Myc t (8q24) negative. Positive immunohistochemistry for ALC, CD-20, CD-79, BCL2, BCL6. Proliferation index of 40% (Ki67).

Given the results of the tumour, it was referred to haematologist for follow-up and treatment. To complete the study, PET-CT with 18-F-FDG was requested. The results showed two hypermetabolic lymphadenopathies in the left pararectal territory and two hypermetabolic nodules in mesenteric fat. In addition, a high-intensity focal deposit was observed in the right thyroid lobe (figure 1).

Figure 1.

Hypermetabolic thyroid lesion on PET-CT extension study.

Investigations

After these findings in PET-CT, a thyroid ultrasound was performed, the results of which (figure 2) showed the presence of a large hypoechoic solid mass with irregular contours with suspected microcalcifications, without peripheral vascularisation and with small implants around the large mass. with high suspicion of malignancy (Thyroid Imaging Reporting and Data System, TIRADS 5). Given the suspicion and history, the nodule was punctured at two different points and the samples were sent to pathological anatomy and haematology, obtaining as a result: Presence of red blood cells and the following leucocyte formula: 3% eosinophils, 13% neutrophils, 71% lymphocytes, 3% monocytes, 10% large lymphoid cells with high core/cytoplasm ratio, slightly irregular contour nucleus, condensed chromatin, occasionally visible nucleoli and sometimes vacuolated cytoplasm. After fluorescent in situ hybridisation (FISH) study in the sample interface, the cellularity analysed presented three copies of BCL-6 (3q27), one of them rearranged. The results of the colon biopsy and thyroid puncture described the same origin of the lymphoma.

Figure 2.

Ultrasound image with high suspicious lesion on right thyroid lobe. LTD, right thyroid lobe; LTI, left thyroid lobe.

In this way, it was finally concluded as diagnosis: diffuse large B cell lymphoma stage IV-A of intestinal origin with thyroid involvement.

Treatment

Chemotherapeutic treatment was started with an cyclophosphamide, doxorubicin, vincristine, prednisone plus rituximab (R-CHOP) scheme with intrathecal prophylaxis (first line of treatment) with good tolerance.

Outcome and follow-up

In the follow-up of the patient, after the second cycle of chemotherapy, a new thyroid ultrasound was performed (figure 3) that showed almost complete disappearance of the hypoechoic mass evidenced in the previous ultrasound, highlighting three small hypoechoic areas in a residual way in the right thyroid lobe (RTL). Two and six millimetres without appearance of nodules or vascularisation (TIRADS 2).

Figure 3.

Ultrasound image without lesion on right thyroid lobe after treatment. LTD, right thyroid lobe. LTI, left thyroid lobe.

After carrying out the third cycle of chemotherapy, PET-CT with control 18-F-FDG was performed, the result of which showed a significant decrease in metabolic activity in RTL, now non-metabolic, without evidence of other hypermetabolic lesions.

Discussion

When a thyroid lesion appears in an imaging test such as PET-CT marked with 18-F-FDG, it is advisable to complement the study with ultrasound, also assessing the need to perform FNA if the imaging test is suggestive of malignancy.^{5 6}

In the confirmation diagnosis of both primary and secondary thyroid lymphoma of another location, it is frequent that the first test to be performed is an FNA, obtaining a yield around 70%–60%. In recent years, the incorporation of immunohistochemical techniques and other additional techniques, such as the PCR or FISH, has allowed to increase the diagnostic capacity of the samples obtained by FNA.⁷

In our case, the result of FNA, supported by immunohistochemistry and FISH, gave us the confirmation diagnosis,⁷ being fundamental not to perform surgery and wait for the response of chemotherapy treatment, since only by ultrasound criteria would surgery have been chosen in this patient.

Diffuse large B cell lymphoma is the most common form of non-Hodgkin’s lymphoma (NHL) in adults and accounts for about 30% of NHL.⁸ There is a marked clinical and biological heterogeneity in this group of lymphoid neoplasms. It is a disease with chemotherapy treatment, with good response to its first-line scheme based on R-CHOP with an estimated survival at 5 years around 60% in cases of disseminated involvement.

Usually, the cases of thyroid metastasis of a lymphoma are associated with invasion in another area,;however, in our case, the patient did not present metastasis in another location, being an exceptional case of single thyroid metastasis.

It is important to highlight the role of FNA guided by ultrasound, which, supported by complementary immunohistochemical and cytogenetic techniques, has been fundamental for the diagnosis of secondary thyroid lymphoma.

Learning points.

• Every thyroid lesion on PET-CT marked with 18F-2-fluoro-2-deoxy-d-glucose, it is usually necessary to complement the study with ultrasound.

• Fine needle aspiration on the thyroid gland is very helpful if the imaging test is suggestive of malignancy.

• Immunohistochemical techniques and fluorescent in situ hybridisation can increase the diagnostic capacity of cytology.

• Chemotherapy is the first-line treatment on a metastatic diffuse large B cell lymphoma.