INTRODUCTION

Radiation changes in lung cytology specimens can lead to diagnostic challenges. Cells with radiation atypia can mimic malignancy and can be called either atypical or outright malignant, especially at on-site evaluation. Radiation changes have been described in detail in surgical pathology, but there is a gap in the cytopathology literature.[1] Features such as two-toning of the cytoplasm, vacuolization of the cytoplasm and nucleus, and cytomegaly with low nuclear: cytoplasmic ratios are the most known radiation changes.[1-4] However, a repair-like change mimicking atypical squamous cells with polygonal cells and dense cytoplasm can be very prominent in radiation changes and can be a more recognizable clue in situations that require rapid recognition, such as on-site evaluation.

We present a case of two patients, both with a prior history of lung malignancy and subsequent radiation treatment. One had a metastatic high-grade undifferentiated pleomorphic sarcoma, and the other had a small cell lung carcinoma. One was thought to be malignant on-site, and one was called atypical. Both had hypocellularity and a prominent repair-like change with polygonal or elongated fiber-like cells and dense cytoplasm mimicking atypical squamous cells. Biopsies for both patients showed fibrotic lung with similar cells; however, no malignancy was identified. The first patient also had bizarre nuclei and degenerative nuclei. The findings for both patients were attributed to radiation.

CASE REPORTS Patient 1

A 66-year-old male with a history of right lateral thigh high-grade pleomorphic undifferentiated sarcoma and multiple recurrences developed a right upper lobe lung nodule. During his treatment course, the patient received radiation to the primary site (right thigh, 6000 centigray [cGy]/30 fractions), right chest wall recurrence (6-year post-initial diagnosis, 5000 cGy/5 fractions), and right upper and lower lung (7-year post-initial diagnosis, 5000 cGy/5 fractions). A summary of his clinical course is placed in Table 1.

Table 1: Clinical course of patient 1.

Timeframe Clinical event 0 years Neoadjuvant chemotherapy for two cycles; surgical resection with negative margins; adjuvant radiation to the tumor bed.
(right thigh, 6000 cGy/30 fractions) 2 years Scans demonstrated a left upper lung nodule; wedge resection was performed. 5 years Computerized tomography scan showed a 1.4 cm right upper lung nodule; a right upper lobe wedge resection was performed with mediastinal hilar lymph node dissection; along the suture line in the right supra-hilar region, a 2.2 cm soft tissue mass appeared. 5 years MRI demonstrated a left thigh mass within the left quadriceps muscle; imaging revealed a 6.5 cm mass in the anterior mediastinum; wide local resection of the soft tissue sarcoma with additional right anterior mediastinal mass resection, en bloc right anterior mediastinal pleurectomy, and en bloc right middle and upper lobar wedge resection. 6 years Right chest wall recurrence (5000 cGy/5 fractions) 7 years Right upper and lower lung (5000 cGy/5 fractions) 7 years 7 months A right upper lobe lung nodule was detected on surveillance imaging. Core biopsy, as well as one fine needle aspiration pass, were performed.

Seven months after the radiation treatment to the lung, a right upper lobe lung nodule was detected on surveillance computerized tomography (CT, Siemens AS Siemens Healthineers, Erlangen, Germany) [Figure 1]. Core biopsy, as well as one fine needle aspiration pass, were performed and deemed adequate on the touch preparations. DiffQuik-stained (Epredia USA, Product Numbers 3303, 3313, and 122-962) slides were created on-site for immediate evaluation. Alcohol-fixed slides were prepared for later Papanicolaou staining (Hologic USA ThinPrep Stain Set 70897-001). Cytology revealed a hypocellular specimen with a significant number of groups displaying a very prominent repair-like arrangement with polygonal or elongated fiber-like cells and dense cytoplasm mimicking atypical squamous cells. The touch preparations were thought to be malignant on-site, and the differential of a squamous lung primary was considered [Figure 2]. Final surgical pathology showed fibrotic lung parenchyma with similar cells and occasional large, bizarre, and degenerative nuclei typical of radiation. No malignancy was identified.

Figure 1: Patient 1 lung computerized tomography: Right upper lobe ill-defined 5-cm lesion suggests radiation fibrosis. However, the lesion is discontinuous with the chest wall and lacks well-defined air bronchograms which raise concern for malignancy. Note mediastinal surgical clips from prior surgery.

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Figure 2: Patient 1. Touch preparations showing a (a) hypocellular sample and (b-c) two different areas of repair-like change. (a) Diff-Quik ×100, scale bar 500 μm; (b) Diff-Quik ×200, scale bar 200 μm; (c) Diff-Quik ×400, scale bar 200 μm. Core biopsy shows (d) fibrotic lung parenchyma and (e) similar cells (blue arrow) and occasional larger, more bizarre nuclei, more typical of radiation change (red arrows). (d) Hematoxylin and eosin (H&E) ×100, scale bar 500 μm; (e) H&E ×400, scale bar 200 μm.

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Patient 2

A 55-year-old female with a past medical history of tobacco use had a history of small cell carcinoma in the left hilum and developed a 5.5 × 4.7 cm left lower lobe mass with a likely malignant pleural effusion on lung CT [Figure 3]. She had undergone radiation twice, 1 year prior at 66 and 50 Gy/fractions, respectively. A summary of her clinical course is presented in Table 2.

Figure 3: Patient 2 lung computerized tomography: Left lower lobe, 5.5 × 4.7 cm mass extending to the pleural surface and associated volume loss. Small left pleural effusion, likely malignant. The scale bar is 50.0 mm.

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Table 2: Clinical course of patient 2.

Timeframe Clinical event 0 year Left hilar mass on chest CT; EBUS FNA from the level 7 lymph node region demonstrated small cell carcinoma;
(concurrent chemotherapy-radiation [66 Gy]) Few months later, 0 year CT showed a new 1 cm nodular left lower lobe lung abnormality; additional radiation and chemotherapy (stereotactic body radiation therapy 50 Gy/5 fractions) 1 year PET showed increased metabolic activity in the left hilum associated with an enlarging area of consolidation. Repeat bronchoscopy with level 10 L lymph node demonstrated small cell carcinoma.
Imaging showed a liver lesion. Metastatic disease was found to be infiltrating the T6 and L3 vertebral bodies.
Lung CT showed a 5.5×4.7 cm left lower lobe mass. 1 year Targeted lung core biopsy and cytology touch preparations were performed.

Targeted lung core biopsy and cytology touch preparations were performed for clinical trial evaluation 1 year after radiation treatment. The touch preparations were deemed satisfactory. Diff-Quik slides were created on-site for immediate evaluation. Alcohol-fixed slides were prepared for Papanicolaou staining. Cytology revealed a hypocellular specimen with a repair-like change similar to patient #1. Nucleoli were more prominent than in patient #1. This was called atypical on-site. Biopsy slides showed fibrosis and similar cells [Figure 4]. The changes were attributed to radiation.

Figure 4: Patient 2. (a) Touch preparations showing a hypocellular specimen with a repair-like change (inset). (a) Diff-Quik ×100 scale bar 500 μm; (insert) Diff Quik ×400 scale bar 200 μm. (b) Core biopsy shows fibrotic lung parenchyma and (c) a different area with similar cells (red arrow). (b) Hematoxylin and eosin (H&E) ×100; scale bar 500 μm, (c) Hematoxylin and Eosin (H&E) ×400, scale bar 200 μm.

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DISCUSSION

The pathological mechanisms of cellular reactivity associated with radiation therapy to the lung have been described.[5] Free radicals are created from ionizing radiation, damaging deoxyribonucleic acid and cellular membranes, leading to cellular malfunction and death. Three phases are associated with the lung’s response to radiation: The acute exudative phase, which occurs 2–3 months after radiation; the proliferative phase, which occurs 2–9 months after radiation; and the chronic fibrotic phase, which occurs more than 9 months after radiation.[5] During the acute phase, you may observe vacuolization, congestion, thrombosis, and hyaline membrane formation.[5] Type II pneumocytes proliferate and can have atypia, such as hyperchromasia and multinucleation. During the intermediate phase, the aforementioned atypia becomes prominent, and there is early deposition of collagen fibrils that lead to fibrosis. Chronic radiation entails fibrosis with loss of atypical cells and hyaline membranes.[5] Radiation changes may resolve within a month after cessation of radiation, but may also persist throughout an individual’s life with dispersed atypical cells.[2,3]

The only articles in the English literature looking at cytology of cases with a history of previous exposure to radiation therapy looked at bronchoalveolar lavages and sputum. Bronchoalveolar lavages in four patients who had unilateral radiation pneumonitis after treatment for carcinoma of the breast showed an increase in cell number and lymphocytosis in both non-irradiated and irradiated lungs.[5,6]

Radiation morphologic changes include cytoplasmic vacuolization, nuclear vacuolization, smudgy degenerative nuclei, prominent nucleoli, and cytomegaly.[1-4] Bizarre cells are also seen post-radiation.[1] Studies have proposed that cytoplasm is sensitive to the effects of radiation, resulting in vacuolization.[1,4] Two-toning of the cytoplasm has also been described.[2] Longatto Filho et al. mention without a photographic example that metaplastic epithelial cells are seen in post-radiation samples, with the main change being metachromasia or pseudo-eosinophilic cytoplasm.[1]

In our two cases, we had to distinguish radiation atypia from malignancy. The time after radiation was 7 months and 1 year for Case #1 and Case #2, respectively. This would correspond to the proliferative and chronic fibrotic phases. The most prominent feature of these cases was a change that mimicked atypical squamous cells with a repair-like arrangement, polygonal or elongated fiber-like cells, dense cytoplasm, and either prominent nucleoli or degenerative nuclei in which nucleoli were not visible. This is similar in appearance to squamous metaplasia but has not been described as such.

Saad and Silverman have shown similar images and have called it reactive bronchial epithelium.[3] We think that they are different from reactive bronchial epithelium. Repair-like changes are not widely discussed in the literature but have been mentioned by Idowu and can be accompanied by vacuolization.[2] Could this repair-like change represent Longatto’s described pseudoeosinophilic metaplastic changes? It is unclear. Full morphologic description and the molecular mechanism by which this occurs are not present in the current literature. A table comparing the differences between this radiation repair-like change and squamous cell carcinoma is provided below [Table 3].[7]

Table 3: Comparison of radiation repair-like changes and squamous cell carcinoma.

Features Radiation repair-like change Squamous cell carcinoma Cellularity Hypocellular Usually, hypercellular Architecture Streaming appearance, less single cells More single cells Shape Elongated, fiber-like, or polygonal Elongated, fiber-like, or polygonal Nuclei Monotonous or bland, round to oval Some pyknotic nuclei, some oval-to-irregular nuclei Chromatin Pale, fine Coarse

Although we emphasize this repair-like change based on our observations, the limitation of this paper is that it is only a report of 2 cases; a larger case series must be performed to determine the real frequency of this occurrence.

The factors that may affect the radiation effect on the lung include the volume of lung irradiated, dose, and dose rate. Doses of <3000 cGy are tolerated, while radiation changes are almost always seen above 4000 cGy and become severe above 5000 cGy.[5] Irradiation of less than half of one lung is usually well-tolerated, while irradiation of both lungs, irradiation of the lower and mid lung zones, and the use of lateral/oblique multidirectional ports can lead to severe radiation changes.[5] For both our cases, more than 5000 cGy was administered.

CONCLUSION

In conclusion, repair-like changes with dense cytoplasm and polygonal or elongated fiber-like cells can be the most prominent feature in radiation changes. These changes can mimic atypical squamous cells. Recognition of repair-like changes in a hypocellular specimen can help a pathologist quickly recognize radiation changes on-site and avoid an atypical or malignant call.

AVAILABILITY OF DATA AND MATERIALS

Data and materials not shared (all data generated or analyzed during this case report are included in this article).

ABBREVIATIONS

cGy: Centigray

cm: centimeters

CT: Computerized Tomography

EBUS: Endobronchial ultrasound

FNA: Fine needle aspiration

Gy: Gray

H&E: Hematoxylin and eosin

mm: millimeters

MRI: Magnetic resonance imaging

AUTHOR CONTRIBUTIONS

BP: Writing, editing, analysis of data; RVR: Wrote original draft, analysis of data; RM: Contribution of radiologic image and description, editing; AA: Editing, interpretation of data; MA: Editing, interpretation of data; MR: Editing, analysis of data; JF: Editing, interpretation of data; MCR: Writing, editing, cytology and histology photo contributor, and conceptualization. All the authors critically reviewed the important academic content and ultimately approved the published version. All the authors were capable of being responsible for all aspects of the work, ensuring that any issues related to the accuracy and completeness of any part of the work were properly investigated and resolved. Each contributor should fully participate in the work to assume the public responsibility for the appropriate content of the manuscript. All the authors have read and approved the final manuscript. All authors are eligible for ICMJE authorship.