Multiple myeloma (MM) is a hematologic cancer which usually manifested by bone pain, hypercalcemia, anemia, lytic bone lesions and monoclonal gammopathy. The co-existence multiple myeloma and another cancer such as renal cell carcinoma, lung, gastric carcinoma, colon, prostate, breast, bladder, uterus, and liver have been reported severally in literature [1] [2] [3][4][5], but medullary thyroid carcinoma (MTC) as a second malignancy with multiple myeloma is an extremely rare case which seems has not been reported before, here we are presenting a case with these two types of cancer.

A 54-year-old male with diabetes history presented on 17th November 2013 with complaints of severe bone pain on his shoulder and vomiting. The physical examination was unremarkable but a primary photo X-ray in emergency room showed abnormal lytic lesions in the bone and pathologic fracture in clavicle (Figure 1) , so he was referred to the oncologist with high suspicious for a malignancy, the primary laboratory investigation revealed ESR:77 mm/h , the skull X-ray showed multiple punched out lesions (Figure 2)

And the whole body scan reported multiple irregular and abnormal uptake in anterior and posterior rib-skull-right shoulder and highly suggestive multiple bone metastasis (Figure 3) in the next laboratory investigation yielded the following findings: βՇ-microglobulin :9.9(1.1–2.4) mg /L, αՇ:17.6 (7.1–11.8) g/L , in his urine electrophoresis, Lambda light chain was 88 (5.9)mg/L, (detailed results laboratory tests are given in Table 1), the aspiration of bone marrow found 25% plasma cells which some were multiple nucleus and others looking plasma blast (detailed reports of bone marrow aspiration is given in Table 2) and biopsy of bone marrow reported that hematopoietic cells have been replaced by proliferation of plasma cells and finally with diagnosis of the multiple myeloma, chemotherapy was initiated for patient with the regiment of VAD (vincristine, adriablastina, , dexamethasone) and zometa.

After four cycles chemotherapy, once more bone marrow aspiration revealed incomplete response to cure with 15 % plasma cells and evaluation of free lambda light chain was 124 (up to 5.9) mg/L so the chemotherapy changed and continued with velzomib, and once more bone marrow aspiration showed mild plasmacytosis 7% and the patient reached a partial remission, about after nine months later, the laboratory tests changed and ESR elevated for second time, during investigation we found a palpable solitary nodule in the thyroid of patient, the thyroid function test showed TSH: 2.6 mlU/L, T4: 8.5 µg/dL and T3:142 ng/dL and ultrasonography of thyroid reported a well-defined hypoechoic solitary nodule in middle of right lobe of thyroid with numerous and small zones of calcification with no adenopathy in neck and suggested for fine needle aspiration (FNA) because it was suspicious for malignancy , in that time some differential diagnosis were made: metastasis of multiple myeloma to thyroid, or primary thyroid malignancy metastasis to bone and our first diagnosis of multiple myeloma could be rejected by this assumption and the last one diagnosis was thyroid malignancy as a secondary cancer. Therefore, the patient underwent FNA which reported medullary thyroid carcinoma with the laboratory test investigation of calcitonin: 268 ng/L, CEA: 78 µg/L, ESR: 63 mm/h and with these evidences the probability of metastatic of primary multiple myeloma ruled out. And with diagnosis of MTC, patient was referred to surgeon and after total thyroidectomy, the histopathology after surgery confirmed medullary thyroid carcinoma (Figure 4).

After surgery the patient was recovered and the laboratory tests return to nearly normal levels. The patient remained in good health and he is followed-up for these malignancies.

Second primary cancer is one of the effective prognostic factors among cancer survivors and it is estimated to be the sixth most common form of malignancy in the world [6], although secondary solid neoplasms in patients with multiple myeloma are rare, but some studies have reported the increasing risk of that. In a study by Stegeman et al., multiple myeloma and solid tumor co-existence was found to be 3% [7] and Kyle at al. reported that, in 1027 patients diagnosed with multiple myeloma, the proportion of secondary hematologic malignity was 0.7% and the proportion secondary solid malignancy was 1.9% [8]. As we mentioned earlier, malignancies synchronized with multiple myeloma have been reported before [1] [2][3][4] [5]. But it was not included medullary thyroid carcinoma which occurs extremely rare, to our knowledge there are no prior reports of this case. The etiology of this correlation in our case is not clear but according to some hypothesis, secondary malignancies associated with MM can be because of behaviors (such as smoking, harmful levels of alcohol consumption and poor diet), inherited susceptibilities and/or the medical treatment that cancer survivors have received [9] [10]. Further investigations would be done in order to understand of whether this secondary malignancy is only accidental or whether there is any cause and effect relationship, another point of this case is about the differential diagnosis of thyroid nodule which was discovered some months after diagnosis multiple myeloma that could be mistaken by metastasis of multiple myeloma to thyroid gland which has been reported severally [11][12][13] or the primary cancer was MTC which could metastasis to bone and mimicked the multiple myeloma and it could change the way of treatment. But pathology samples and the elevation of laboratory markers such as calcitonin level excluded it and responding to cure and remission after total thyroidectomy, ruled out the second suspicious diagnosis. And another things which should be kept in mind in these kind of cases, try to investigate and pay attention to the new signs and symptoms which set during disease and may not be related to the primary cancer or complications of it, and another associated disease should be considered even if it is too unusual. In this case, patient reached to remission after chemotherapy but once more elevated ESR caused to investigate more.

A rare correlation between multiple myeloma and medullary thyroid carcinoma case is reported, diagnosis of secondary cancer is important because: first: to distinguish secondary malignancy from metastatic cancer then try to investigate the etiology of this association and finally to determine to choose the best treatment because of its good prognosis.

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